A system and method for utilizing inter-cell multiplexing gain in a wireless cellular system via distributed input / distributed output technology.

Abstract

This system utilizes inter-cell multiplexing gain through spatial processing of wireless communication networks. [Solution] A multiple antenna system (MAS) with multi-user (MU) transmission ("MU-MAS") that increases the capacity of a wireless communication network by utilizing inter-cell multiplexing gain through spatial processing. Over the past 30 years, the wireless cellular market has experienced a global increase in subscriber numbers, as well as a demand for better services shifting from voice to web browsing and real-time HD video streaming. This increasing demand for services requiring higher data rates, lower latency, and improved reliability has driven the rapid evolution of wireless technology through different standards.

Description

Technical Field

[0001] [Related Applications] This application may be related to the following co-pending U.S. patent applications / U.S. patents.

[0002] U.S. Patent Application No. 13 / 633,702, titled "Systems and Methods for wireless backhaul in distributed-input distributed-output wireless systems".

[0003] U.S. Patent Application No. 13 / 475,598, titled "Systems and Methods to enhance spatial diversity in distributed-input distributed-output wireless systems".

[0004] U.S. Patent Application No. 13 / 233,006, titled "System and Methods for planned evolution and obsolescence of multiuser spectrum".

[0005] U.S. Patent Application No. 13 / 232,996, titled "Systems and Methods to Exploit Areas of Coherence in Wireless Systems".

[0006] U.S. Patent Application No. 13 / 464,648, titled "System and Methods to Compensate for Doppler Effects in Distributed-Input Distributed Output Systems".

[0007] U.S. Patent Application No. 12 / 917,257, titled "Systems and Methods To Coordinate Transmissions In Distributed Wireless Systems Via User Clustering".

[0008] U.S. Patent Application No. 12 / 802,988, titled "Interference Management, Handoff, Power Control and Link Adaptation in Distributed-Input Distributed-Output (DIDO) Communication Systems".

[0009] U.S. Patent Application No. 12 / 802,974, titled "System and Method for Managing Inter-Cluster Handoff Of Clients Which Traverse Multiple DIDO Clusters".

[0010] U.S. Patent Application No. 12 / 802,989, titled "System and Method for Managing Handoff Of A Client Between Different Distributed-Input-Distributed-Output (DIDO) Networks Based On Detected Velocity Of The Client".

[0011] U.S. Patent Application No. 12 / 802,958, titled "System and Method For Power Control and Antenna Grouping In A Distributed-Input-Distributed-Output (DIDO) Network".

[0012] U.S. Patent Application No. 12 / 802,975, title: "System and Method For Link Adaptation In DIDO Multicarrier Systems".

[0013] U.S. Patent Application No. 12 / 802,938, title: "System and Method For DIDO Precoding Interpolation In Multicarrier Systems".

[0014] U.S. Patent Application No. 12 / 630,627, title: "System and Method For Distributed Antenna Wireless Communications".

[0015] U.S. Patent No. 8,170,081, issued May 1, 2012, titled "System and Method For Adjusting DIDO Interference Cancellation Based on Signal Strength Measurements".

[0016] U.S. Patent No. 8,160,121, issued April 17, 2012, titled "System and Method For Distributed Input-Distributed Output Wireless Communications".

[0017] U.S. Patent No. 7,885,354, issued on February 8, 2011, titled "System and Method For Enhancing Near Vertical Incidence Skywave ("NVIS") Communication Using Space-Time Coding".

[0018] U.S. Patent No. 7,711,030, issued May 4, 2010, titled "System and Method For Spatial-Multiplexed Tropospheric Scatter Communications".

[0019] U.S. Patent No. 7,636,381, issued December 22, 2009, titled "System and Method for Distributed Input Distributed Output Wireless Communication".

[0020] U.S. Patent No. 7,633,994, issued December 15, 2009, titled "System and Method for Distributed Input Distributed Output Wireless Communication".

[0021] U.S. Patent No. 7,599,420, issued October 6, 2009, titled "System and Method for Distributed Input Distributed Output Wireless Communication".

[0022] U.S. Patent No. 7,418,053, issued August 26, 2008, titled "System and Method for Distributed Input Distributed Output Wireless Communication". [Background technology]

[0023] Over the past 30 years, the wireless cellular market has experienced a global increase in subscriber numbers and a growing demand for better services, shifting from voice to web browsing and real-time HD video streaming. This increasing demand for services requiring higher data rates, lower latency, and improved reliability has driven the rapid evolution of wireless technology through various standards. Beginning with the first generation analog AMPS and TACS (for voice services) in the early 1980s, followed by 2G and 2.5G digital GSM®, IS-95 and GPRS (for voice and data services) in the 1990s, 3G with UMTS and CDMA2000 (for web browsing) in the early 2000s, and finally, LTE (for high-speed internet connectivity), which is now deployed in various countries around the world.

[0024] Long-Term Evolution (LTE) is a standard developed by the 3rd Generation Partnership Project for Fourth Generation (4G) Wireless Cellular Systems (3GPP). Theoretically, LTE can achieve up to four times the downlink spectral efficiency compared to previous 3G and HSPA+ standards by utilizing the spatial components of the wireless channel through Multiple Input Multiple Output (MIMO) technology. LTE-Advanced is an advanced version of LTE, currently under standardization, and theoretically will enable up to eight times the spectral efficiency compared to 3G standard systems.

[0025] Despite the evolution of this technology, in the next three years, wireless carriers are likely to struggle to meet the increasing demand for data rates due to the growing market penetration of smartphones and tablets that provide more data-intensive applications such as real-time HD video streaming, video conferencing, and gaming. The capacity of wireless networks is expected to expand five-fold in Europe from 2011 to 2015

[25] due to improved technologies such as LTE and additional spectrum made available by governments. For example, the FCC plans to free up 500 MHz of spectrum by 2020 (300 MHz of which will be available by 2015) to promote wireless Internet connectivity across the United States as part of the National Broadband Plan

[24] . Unfortunately, the projected capacity usage by 2015 is 23 times that in 2011 in Europe

[25] , and a similar spectrum shortage is expected to occur in the United States by 2014 [26 - 27]. As a result of this data crisis, the revenues of wireless carriers may fall below their capital expenditure (CAPEX) and operating expenses (OPEX), potentially having a disruptive impact on the wireless market

[28] .

[0026] Due to the insufficient capacity gains provided by the deployment of LTE and increased spectrum availability, the only foreseeable solution to prevent this impending spectrum crisis is to drive new wireless technologies forward

[29] . LTE-Advanced (an evolved version of the LTE standard) promises further gains over LTE by means of more advanced MIMO technologies and by increasing the density of "small cells"

[30] . However, there is a limit to the number of cells that can be adapted to a particular area without introducing interference problems or increasing the complexity of the backhaul in order to enable cooperation between cells.

[0027] Without the constraints of conventional cellular systems, one promising technology that provides a large increase in spectral efficiency over wireless links is the distributed input distributed output (DIDO) technology (see related patents and applications cited in [0002 - 0020] above). To provide significant performance benefits over conventional wireless systems, the present invention describes DIDO technology used in relation to cellular systems (such as LTE or LTE - Advanced), both within and outside the constraints of cellular standards. Beginning with an overview of MIMO, various spatial processing techniques used by LTE and LTE - Advanced are examined. Next, the present invention shows how to provide significant capacity gains for next - generation wireless communication systems compared to conventional approaches.

[0028] MIMO uses multiple antennas at the transmitter and receiver sides of a wireless link to improve link reliability by diversity techniques (i.e., diversity gain) or to provide a higher data rate by multiplexing techniques (i.e., multiplexing gain) using spatial processing [1 - 2]. Diversity gain is a measure of enhanced robustness against signal fading and results in a higher signal - to - noise ratio (SNR) for a fixed data rate. Multiplexing gain is obtained by exploiting additional spatial degrees of freedom of the wireless channel to increase the data rate at a fixed error probability. The basic trade - off between diversity and multiplexing in a MIMO system is described in [3 - 4].

[0029] In practical MIMO systems, link adaptive techniques can be used to dynamically switch between diversity and multiplexing schemes based on propagation conditions [20-23]. For example, the link adaptive techniques described in [22-23] showed that beamforming or orthogonal space-time block coding (OSTBC) is a preferred scheme in low-SNR regimes or channels characterized by low spatial selectivity. On the other hand, spatial multiplexing can provide significant gains in data rates for channels with high SNR and high spatial selectivity. For example, Figure 1 shows that a cell can be divided into two regions: i) a multiplexing region 101 characterized by high SNR (due to proximity to the cell tower or base station) where the spatial degrees of freedom of the channel can be utilized by spatial multiplexing to increase the data rate; and ii) a diversity region 102 or cell edge where spatial multiplexing techniques are not so effective and diversity methods can be used to improve SNR and coverage (producing only a small increase in data rate). Note that in Figure 1, the shaded central area of ​​the macrocell is labeled as the "multiplexing region," while the unshaded outer area is labeled as the "diversity region." This same regional designation—that the shaded area is the "multiplexing region" and the unshaded area is the "diversity region"—is used throughout Figures 1 and 3-5, even if the area is not explicitly labeled. For example, the same designation is also used for subcell 104 in Figure 1.

[0030] The LTE (Release 8) and LTE-Advanced (Release 10) standards define a set of 10 transmission modes™, which include either diversity or multiplexing schemes [35, 85-86]. Mode 1. Single antenna port, port 0 Mode 2. Transmit diversity. Mode 3. Extensions to open-loop space multiplexing for large-delay cyclic-delay diversity (CDD) and single-user MIMO (SU-MIMO). Mode 4. Closed-loop spatial multiplexing for SU-MIMO. Mode 5. Multi-user MIMO (MU-MIMO) Mode 6. Closed-loop spatial multiplexing, using a single transmit layer. Mode 7. Single antenna port, UE-specific RS (port 5) Mode 8. Single or dual-layer transmission, UE-specific RS (ports 7 and / or 8) • Mode 9. Single or up to 8 layers of closed-loop SU-MIMO (added in Release 10) • Mode 10: Multi-layer closed-loop SU-MIMO with up to 8 layers (added in Release 10)

[0031] Below, we describe the diversity and multiplexing schemes commonly used in cellular systems, as well as the specific methods used in LTE outlined above, and compare them with technologies specific to DIDO communication. First, we identify two types of transmission methods: i) intracell methods (utilizing microdiversity in cellular systems) that use multiple antennas to improve link reliability or data rate within a single cell, and ii) intercell methods (utilizing macrodiversity) that enable coordination between cells to provide additional diversity or multiplexing gain. Next, we describe methods in which the present invention offers significant advantages (including spectral capacity gain) over the prior art.

[0032] 1. Intracell Diversity Methods Intracell diversity methods operate within a single cell and are designed to enhance the signal-to-noise ratio (SNR) in scenarios with poor link quality (e.g., users at the cell edge experiencing high path loss from the central tower or base station). Typical diversity methods used in MIMO communications include beamforming [5-11] and orthogonal space-time block coding (OSTBC) [12-15].

[0033] The diversity technologies supported by the LTE standard are transmit diversity, closed-loop rank-1 precoding, and dedicated beamforming [31-35]. Transmit diversity supports two or four transmit antennas on the downlink (DL) and only two antennas on the uplink (UL). It is implemented in the DL channel by spatial frequency block coding (SFBC) combined with frequency switching transmit diversity (FSTD) to take advantage of spatial and frequency selectivity

[31] . Rank-1 precoding generates a dedicated beam for one user based on quantized weights selected from a codebook (pre-designed using limited feedback techniques [36-42]) to reduce feedback overhead from the user equipment (UE) to the transmit / receive base station (BTS 105 in Figure 1, i.e., eNodeB in LTE terminology). Alternatively, dedicated beamforming weights can be calculated based on a UE-specific reference signal.

[0034] 2. Intracell Multiplexing Method MIMO multiplexing schemes [1, 19] provide data rate gains in high SNR regimes and in scenarios with sufficient spatial freedom in the channel (e.g., rich multipath environments with high spatial selectivity [16-18]) in order to support multiple parallel data streams on a wireless link.

[0035] The LTE standard supports various multiplexing techniques for single-user MIMO (SU-MIMO) and multi-user MIMO (MU-MIMO)

[31] . The SU-MIMO scheme has two operating modes: i) Closed-loop, which utilizes feedback information from the UE to select DL precoding weights; ii) Open-loop, which is used when feedback from the UE is unavailable or when the UE is moving too fast to support the closed-loop scheme. The closed-loop scheme uses a set of pre-calculated weights selected from a codebook. These weights can support two or four transmitting antennas, as well as one to four parallel data streams (specified by the number of layers in the precoding matrix), depending on the UE's request and the BTS scheduler's judgment. LTE-Advanced can include new transmission modes up to MIMO 8x8 to provide up to an 8x increase in spectral efficiency through spatial processing

[62] .

[0036] The MU-MIMO scheme is defined for both UL and DL channels [31, 50]. In UL, every UE sends a reference signal (consisting of a cyclically shifted version of the Zadoff-Chu sequence

[33] ) to the BTS. These reference signals are orthogonal so that the BTS can estimate the channels from all UEs and demodulate data streams from multiple UEs simultaneously through spatial processing. In DL, precoding weights for various UEs are selected from a codebook based on feedback from the UEs and the scheduler (similar to the closed-loop SU-MIMO scheme), and only rank-1 precoding is possible for every UE (e.g., each UE receives only one data stream).

[0037] Intracell multiplexing techniques using spatial processing offer good performance only in propagation scenarios characterized by high SNR (or SINR) and high spatial selectivity (multipath-rich environments). For conventional macrocells, these conditions can be more difficult to achieve because the BTS is typically far from the UE and the SINR distribution is typically concentrated at low values ​​

[43] . In these scenarios, MU-MIMO or diversity techniques may be a better choice than SU-MIMO with spatial multiplexing.

[0038] Another technology and network solution conceivable by LTE-Advanced to achieve further multiplexing gain (without requiring spatial processing by MIMO) is carrier aggregation (CA) and small cells. CA[30, 44-47] combines different parts of the RF spectrum to increase signal bandwidth up to 100 MHz

[85] , thereby giving higher data rates. Intraband CA combines different bands within the same portion of the spectrum. Thus, it can use the same RF chain for multiple channels, and the multiple data streams are recombined in software. Interband CA requires different RF chains to operate in different portions of the spectrum and also requires signal processing to recombine multiple data streams from different bands.

[0039] The main idea behind small cells [30, 47] is to reduce the size of conventional macrocells, thereby enabling higher cell density and greater throughput per area of ​​coverage. Small cells are typically deployed through inexpensive access points 106 with low-power transmission (as shown in Figure 1), in contrast to the tall, expensive cell towers used for macrocells. Two types of small cells are defined in LTE-Advanced: i) metrocells for outdoor installations in urban areas, supporting 32 to 64 concurrent users; and ii) femtocells for indoor use, capable of supporting up to 4 active users. One advantage of small cells is the statistically higher density of UEs near the BTS, thereby giving better SNR which can be utilized through spatial multiplexing to augment data rates. However, there are still many concerns regarding the practical deployment of small cells, particularly those related to backhaul. In fact, reaching any small cell's BTS through high-speed wired connections may be challenging, especially considering the high densities of metrocells and femtocells in a given area of ​​coverage. Compared to wired backhaul, using line-of-sight (LOS) backhaul for small cells is often less expensive, but there are often no practical LOS backhaul paths available for the preferred small cell BTS placement, and there is no general solution for non-line-of-sight (NLO) wireless backhaul to small cell BTS. Furthermore, small cells require complex real-time coordination between BTS to avoid interference, as in self-organizing networks (SONs) [30, 51-52], and require advanced cell planning tools (which are even more complex than conventional cellular systems due to the high density of small cells) to plan their optimal locations [48, 49]. Finally, handoff is a limiting factor in small cell deployment, especially in scenarios where multiple groups of subscribers switch cells simultaneously, causing a large overhead handoff across the backhaul, resulting in long wait times and unavoidable missed calls.

[0040] It can be shown self-evidently that there is no practical general solution that enables small cells to coexist with macrocells and achieve optimal or necessarily improved throughput. One of countless such intractable situations is when a small cell is positioned such that its UE inevitably overlaps with macrocell transmission, and both the small cell and macrocell use the same frequency to reach their respective UEs. In this situation, macrocell transmission will obviously interfere with small cell transmission. There may be some approaches to mitigate such interference in specific circumstances, such as specific macrocells, specific small cells, specific macrocell and small cell UEs involved, the throughput requirements of those UEs, and environmental conditions. However, any such approach is highly specific, not only for static planning of macrocells and small cells, but also for dynamic situations over specific time intervals. Typically, full channel throughput for each UE is not achievable.

[0041] 3. Intercellular diversity methods In heterogeneous networks (HetNets)

[90] , where macrocells coexist with smaller cells (e.g., metrocells, picocells, and femtocells), various techniques must be employed to eliminate inter-cell interference. While HetNets offer better coverage through smaller cells, the gain in data rate is minimal because they require sharing the spectrum through different forms of frequency repeating patterns or using spatial processing to eliminate interference rather than gaining multiplexing gain. LTE standards utilize inter-cell interference control (ICIC) schemes to eliminate interference, particularly at the cell edges. There are two types of ICIC methods: cell-agnostic and coordinated between BTSs.

[0042] The cell-autonomous ICIC scheme avoids inter-cell interference through different frequency repetition patterns, as shown in Figure 2. In Figure 2, hexagons represent cells, and colors represent different carrier frequencies. Three schemes are being considered for LTE: i) full frequency repetition (or repetition 1), where cells use all available bandwidth, generating high interference at the cell edges, as shown in Figure 2a; ii) hard frequency repetition (HFR), where different frequency bands are assigned to each cell (typically with a repetition factor of 3), as shown in Figure 2b; and iii) fractional frequency repetition (FFR), where the center of the cell is assigned to the entire available bandwidth, like frequency repetition 1, while the cell edges operate in HFR mode to mitigate inter-cell interference, as shown in Figure 2c.

[0043] The Coordinated ICIC method enables coordination between BTSs to improve the performance of the wireless network. These techniques are special cases of the methods taught in related patents and applications [0002-0022] to enable coordination between wireless transceivers in the common case of a distributed antenna network for multiplexed UEs where all are using the same frequency simultaneously. Coordination between BTSs to eliminate inter-cell interference for a specific case of a cellular system relating to a single UE at a given frequency and a given time is described in

[53] . The system in

[53] divides any macrocell into multiple subcells and enables flexible handoff between subcells by using dedicated beamforming from coordinated BTSs. And by using dedicated beamforming from coordinated BTSs, the robustness of the link at a single frequency and a single UE is improved as the single UE moves along the subcell boundary.

[0044] Recently, this class of cooperative wireless cellular networks has been clearly defined in the MIMO literature as "Network MIMO (MIMO)" or "Cooperative Multipoint" (CoMP) systems. Theoretical analyses and simulated results regarding the benefits of Network MIMO by eliminating inter-cell interference are shown in [54-61]. The advantage of Network MIMO and CoMP is that, for macrocell 302, inter-cell interference in the cell overlap region labeled "interference region" 301 in Figure 3 is eliminated.

[0045] CoMP networks are actively becoming part of the LTE-Advanced standard as a solution to mitigate inter-cell interference in next-generation cellular networks [62-64]. Three CoMP solutions have been proposed in the standard to eliminate inter-cell interference: i) Coordinated Scheduling / Beamforming (CS / CB), in which a UE receives its data stream via beamforming from only one BTS, and coordination across BTS makes interference elimination possible via beamforming or scheduling techniques; ii) Dynamic Cell Selection (DCS), in which cells are dynamically selected on a subframe basis transparently to the UE for any UE; and iii) Joint Transmission (JT), in which data for a given UE is transmitted jointly from multiple BTS to improve the received signal quality and eliminate inter-cell interference. CoMP-JT yields greater gains than CoMP-CS / CB at the expense of higher overhead in backhaul to enable coordination between BTS.

[0046] 4. Intercell Multiplexing Method Prior art multi-user wireless systems add complexity and constraints to wireless networks, resulting in a situation where a given user's experience (e.g., available throughput, latency, predictability, reliability) is affected by the use of the spectrum by other users in that domain. Given the increasing demand for total throughput within the wireless spectrum shared by multiple users, and the growing number of applications that can rely on the reliability, predictability, and low latency of a multi-user wireless network for a given user, it is clear that prior art multi-user wireless technologies are subject to many constraints. Indeed, with respect to the limited availability of spectrum suitable for certain types of wireless communication (e.g., at wavelengths effective for penetrating building walls), prior art wireless technologies would be insufficient to meet the increasing demand for bandwidth that is reliable, predictable, and low latency.

[0047] Prior art intra-cell diversity and multiplexing methods can theoretically provide up to a fourfold increase in throughput on current cellular networks (with MIMO 4x4) for LTE, and at most an eightfold increase for LTE-Advanced (with MIMO 8x8). Furthermore, for higher-order MIMO, the improvement in throughput decreases in given multipath environments, especially as UEs (such as smartphones) become smaller and more constrained in terms of antenna placement. Other slight throughput gains in next-generation cellular systems may come from further spectral allocation utilized by carrier aggregation techniques (e.g., the FCC National Broadband Programme), and from higher density distributions of BTSs by small cell networks and SONs ​​[30, 46]. However, all of the above techniques still heavily rely on spectral or time-sharing techniques that enable multi-user transmission, as the spectral efficiency gains obtained by spatial processing are limited.

[0048] Prior art intercell methods (e.g., network MIMO and CoMP systems [53-64]) can improve the reliability of cellular networks by eliminating intercell interference, but their capacity gain is minimal. In fact, these systems are only effective in eliminating intercell interference due to power leakage between cells by restricting the power transmitted from any BTS contained within the cell boundary. Figure 3 shows an example of a cellular network with three BTS, each characterized by its own coverage region or cell. The power transmitted from each BTS is restricted to limit the amount of intercell interference represented in Figure 3 by the region where the cells overlap. Since these systems operate in a low SINR regime in the interference region, their spectral efficiency gain is minimal, similar to intracell schemes for SU-MIMO. To obtain truly significant capacity gain in intercell cooperative networks, the power limitations limited to cell boundaries must be relaxed. Spatial multiplexing techniques must be enabled throughout the cell, not just at the cell edges with poor SINR performance, as in conventional approaches.

[0049] Figure 4 shows that the power transmitted simultaneously from all three BTS 401 at the same frequency is amplified, thereby enabling a high level of interference throughout cell 402. In prior art systems, such interference results in incoherent interference (hindering UE signal reception) throughout the interference region of the BTS, but this interference is actually utilized in the present invention by a new inter-cell multiplexing method. This method uses spatial processing to generate a region of coherent interference (enhancing UE signal reception) around every UE, thereby simultaneously providing every UE with a non-interfering data stream and increasing their SINR through the cell.

[0050] The scenario illustrated in Figure 4 is described in

[89] for a specific case of a cellular system. The system in

[89] consists of several BTSs that identify various cells grouped into clusters. Coordination is permitted only between BTSs from adjacent cells within the same cluster. In this case, it has been shown that as the power transmitted from the BTS increases, there is a limit to the capacity (or spectral efficiency) that can be obtained by the inter-cell multiplexing method. In fact, as the transmitted power increases, the out-of-cluster interference increases proportionally, creating a saturation regime for SINR, and consequently for capacity. As a result of this effect, the system in

[89] can theoretically obtain up to a 3x increase in capacity (i.e., up to 3 cells in a cluster), and any additional cells included in the cluster will have their capacity reduced by the increased out-of-cluster interference (e.g., 21 cells per cluster will yield lower capacity than 3 cells per cluster). We observed that the fundamental capacity limit in

[89] is maintained because the BTS are confined to predetermined locations, as in a cellular system, and the multiplexing gain is obtained by the increasing transmitted power from the BTS. To obtain theoretically infinite capacity through intercell multiplexing methods, constraints on BTS placement must be eliminated, which is advantageous as it allows BTS to be placed anywhere.

[0051] Therefore, it is desirable to provide a system that achieves a large increase in spectral efficiency by utilizing inter-cell multiplexing gain through spatial processing, by removing any power constraints transmitted from the distributed BTS 501 in addition to the constraints on their placement. Figure 5 shows an example in which one many further access points 502 are added to deliberately increase the level of incoherent interference throughout the cell 503. It is utilized in the present invention to generate a region of coherent interference around the UE, thereby giving theoretically infinite inter-cell multiplexing gain. The additional access points are incidentally placed in convenient locations and are not constrained by any particular cell design as in the cellular systems described in the prior art. In exemplary embodiments of the invention, the incidental access points are access points of a distributed input distributed output (DIDO), and the inter-cell multiplexing gain is obtained by the DIDO method described in paragraphs [0014~0020] and [77~78]. In another embodiment, these incidental access points are inexpensive Wi-Fi access points or low-power transceivers similar to small cells [30,47], thereby providing smaller areas of overlapping coverage within the macrocell, as shown in Figure 5.

[0052] It can be seen that prior art intercell methods [53-64] avoid incoherent interference by deliberately limiting the transmit power from all BTS as shown in Figure 3, and remove the remaining intercell interference (with respect to the overlap region between cells) by spatial processing, thereby providing an improved SINR and intercell diversity gain. Furthermore,

[89] limits the capacity obtained by out-of-cluster interference by restricting the BTS placement to the cell design while increasing the transmit power, and thus it is observed that it is still limited by interference. On the other hand, the present invention utilizes incoherent interference by transmitting higher power from any BTS that are placed by chance in order to generate coherent interference around the UE. This improves the signal quality at the UE, which is a prerequisite for obtaining intercell multiplexing gain across the entire cell by spatial processing. Therefore, since there is not enough SINR through the cell (due to limited transmit power from BTS or out-of-cluster interference when transmit power is increased) to enable an intercell multiplexing method such as the present invention, the systems described in the prior art cannot be used to achieve unlimited intercell multiplexing gain by spatial processing. Furthermore, considering that the systems described in the prior art avoid inter-cell interference in the diversity region shown in the shaded areas of Figures 1 and 3-5, rather than utilizing inter-cell interference in the multiplexing region to obtain the inter-cell multiplexing gain realized in the present invention, it is impossible to implement the prior art systems in a way that achieves the multiplexing gain realized in the present invention as shown in Figures 4-5. This invention can be better understood from the following detailed description along with the drawings. [Brief explanation of the drawing]

[0053] [Figure 1] The multiplexing and diversity areas for macrocells and subcells are illustrated. [Figure 2a] The complete frequency repetition pattern in a conventional cellular system is illustrated. [Figure 2b]The hard frequency repetition rate (HFR) pattern in a conventional cellular system is illustrated. [Figure 2c] The fractional frequency repetition rate (FFR) pattern in a conventional cellular system is illustrated. [Figure 3] The interference region between adjacent macrocells is illustrated. [Figure 4] The diagram illustrates multiple BTSs that transmit at high power to increase the interference level between cells. [Figure 5] An example is illustrated in which many access points are added to intentionally increase the level of incoherent interference throughout the cell. [Figure 6] This diagram illustrates the network elements in an LTE network. [Figure 7a] The LTE frame structure for FDD operation is illustrated. [Figure 7b] The LTE frame structure for TDD operation is illustrated. [Figure 8a] This diagram illustrates the LTE "resource elements" and "resource blocks" in an OFDM DL channel. [Figure 8b] This diagram illustrates the LTE "resource elements" and "resource blocks" in the SC-FDMA UL channel. [Figure 9] An embodiment of a multi-user (MU) multiple antenna system (MAS) or MU-MAS, consisting of an antenna cluster and a user cluster, is illustrated. [Figure 10] An embodiment of MU-MAS is illustrated, in which different cell IDs are associated with each antenna subcluster. [Figure 11] An embodiment of MU-MAS is illustrated, in which identical sets of cell IDs are assigned to antenna subclusters in a predetermined repeating pattern. [Figure 12] This diagram illustrates the SNR distribution required for the actual deployment of the MU-MAS system in California, specifically in the urban area of ​​San Francisco, which has both sparsely populated and densely populated regions. [Figure 13]An embodiment of MU-MAS consisting of a CP, a distributed BTS, and multiple UEs is illustrated. [Figure 14] An embodiment of MU-MAS is illustrated, comprising a CP, a distributed BTS, multiple devices, and a single UE connected to the multiple devices and the BTS via a network interface. [Figure 15] This diagram illustrates one embodiment of MU-MAS, in which the UE is located within a case that is physically mounted on the user device. [Modes for carrying out the invention]

[0054] One solution that overcomes many of the limitations of the prior art described above is an embodiment of Distributed Input Distributed Output (DIDO) technology. DIDO technology is described in the following patents and patent applications, all of which have been assigned to the assignee of this patent and are incorporated herein by reference. These patents and applications are referred to several times herein collectively as “Related Patents and Applications.”

[0055] U.S. Patent Application No. 13 / 633,702, title: "Systems and Methods for wireless backhaul in distributed-input distributed-output wireless systems."

[0056] U.S. Patent Application No. 13 / 475,598, titled "Systems and Methods to enhance spatial diversity in distributed-input distributed-output wireless systems."

[0057] U.S. Patent Application No. 13 / 233,006, title: "System and Methods for planned evolution and obsolescence of multiuser spectrum".

[0058] U.S. Patent Application No. 13 / 232,996, title: "Systems and Methods to Exploit Areas of Coherence in Wireless Systems".

[0059] U.S. Patent Application No. 13 / 464,648, titled "System and Methods to Compensate for Doppler Effects in Distributed-Input Distributed Output Systems".

[0060] U.S. Patent Application No. 12 / 917,257, titled "Systems and Methods To Coordinate Transmissions In Distributed Wireless Systems Via User Clustering".

[0061] U.S. Patent Application No. 12 / 802,988, titled "Interference Management, Handoff, Power Control and Link Adaptation in Distributed-Input Distributed-Output (DIDO) Communication Systems".

[0062] U.S. Patent Application No. 12 / 802,974, titled "System and Method for Managing Inter-Cluster Handoff Of Clients Which Traverse Multiple DIDO Clusters".

[0063] U.S. Patent Application No. 12 / 802,989, titled "System and Method for Managing Handoff Of A Client Between Different Distributed-Input-Distributed-Output (DIDO) Networks Based On Detected Velocity Of The Client".

[0064] U.S. Patent Application No. 12 / 802,958, titled "System and Method For Power Control and Antenna Grouping In A Distributed-Input-Distributed-Output (DIDO) Network".

[0065] U.S. Patent Application No. 12 / 802,975, title: "System and Method For Link Adaptation In DIDO Multicarrier Systems".

[0066] U.S. Patent Application No. 12 / 802,938, title: "System and Method For DIDO Precoding Interpolation In Multicarrier Systems".

[0067] U.S. Patent Application No. 12 / 630,627, title: "System and Method For Distributed Antenna Wireless Communications".

[0068] U.S. Patent No. 8,170,081, issued May 1, 2012, titled "System and Method For Adjusting DIDO Interference Cancellation Based on Signal Strength Measurements".

[0069] U.S. Patent No. 8,160,121, issued April 17, 2012, titled "System and Method For Distributed Input-Distributed Output Wireless Communications".

[0070] U.S. Patent No. 7,885,354, issued on February 8, 2011, titled "System and Method For Enhancing Near Vertical Incidence Skywave ("NVIS") Communication Using Space-Time Coding".

[0071] U.S. Patent No. 7,711,030, issued May 4, 2010, titled "System and Method For Spatial-Multiplexed Tropospheric Scatter Communications".

[0072] U.S. Patent No. 7,636,381, issued December 22, 2009, titled "System and Method for Distributed Input Distributed Output Wireless Communication".

[0073] U.S. Patent No. 7,633,994, issued December 15, 2009, titled "System and Method for Distributed Input Distributed Output Wireless Communication".

[0074] U.S. Patent No. 7,599,420, issued October 6, 2009, titled "System and Method for Distributed Input Distributed Output Wireless Communication".

[0075] U.S. Patent No. 7,418,053, issued August 26, 2008, titled "System and Method for Distributed Input Distributed Output Wireless Communication".

[0076] To reduce the volume and complexity of this patent application, some disclosures in related patents and applications are not explicitly described below. For a complete description of those disclosures, please refer to the related patents and applications.

[0077] This invention describes a system and method for utilizing inter-cell multiplexing gain through spatial processing of a wireless communication network, using a multiple-antenna system (MAS) (multi-user multiplexed antenna system, i.e., "MU-MAS") in which multiple antennas are randomly positioned and have multi-user (MU) transmission. In one embodiment of the present invention, the power transmitted from the multiple antennas is constrained to minimize interference at cell boundaries (as in a conventional cellular system), and the spatial processing method is used solely to eliminate inter-cell interference. In another embodiment of the present invention, the power transmitted from multiplexed antennas is not constrained to any particular power level (as long as their power emission levels fall within regulatory, safety, or actual limits (e.g., available power, transmitter, and / or antenna specifications)). Thereafter, higher-order inter-cell interference is deliberately generated through the cells used to achieve inter-cell multiplexing gain, thereby increasing the capacity of the wireless communication network.

[0078] In one embodiment, the wireless communication network is a cellular network, such as a cellular network based on the LTE standard, as shown in Figures 1 and 3, where multiple incidentally deployed antennas are transceivers for macrocells or small cells. In another embodiment of the present invention, the wireless communication network is not constrained to any particular cell layout, and cell boundaries can extend across a larger area, as shown in Figures 4-5. For example, the wireless communication network could be a wireless local area network (WLAN) where multiple antennas are Wifi access points, or a mesh, ad-hoc, or sensor network, or a distributed antenna system, or a DIDO system with incidentally placed access points without any transmit power limitations. However, such examples of network structures should not be considered as limiting the general application of the present invention to wireless communication networks. The present invention applies to any wireless network in which multiplexing gain is achieved by transmitting signals from multiple antennas. These signals interfere where they are received by multiple UEs, generating simultaneous non-interfering data streams to the multiple UEs.

[0079] MU-MAS consists of a centralized processor, a network, and M transceiver stations (or distributed antennas) that communicate wirelessly with N client devices or UEs. The centralized processor unit receives N streams of information (e.g., video, web pages, video games, text, audio, etc., from a web server or other network source) for various client devices with respect to various network content. Hereafter, we will use the term “stream of information” to refer to any stream of data transmitted over the network. It contains information that can be demodulated or decoded like a standalone stream according to a specific modulation / coding scheme or protocol to generate any data, including but not limited to audio, web, and video content. In one embodiment, the stream of information is a set of bits carrying network content that can be demodulated or decoded like a standalone stream.

[0080] A centralized processor utilizes a precoding transform to combine N streams of information from network content into a stream of M bits (by algorithms such as those described in the relevant patents and applications). The precoding transform can be linear (e.g., zero-forcing

[65] , block diagonalization [66-67], matrix inversion, etc.) or nonlinear (e.g., dirty paper coding [68-70] or Tomlinson-Harashima precoding [71-72], lattice techniques or trellis precoding [73-74], vector perturbation techniques [75-76]). Hereafter, the term “stream of bits” refers to any sequence of bits that does not necessarily contain any useful bits of information, and therefore cannot be decoded or demodulated as a standalone stream for reading network content. In one embodiment of the present invention, the stream of bits is a complex baseband signal generated by a centralized processor, quantized to a predetermined number of bits, and transmitted to one of M transmitting and receiving base stations.

[0081] Precoding is computed by a centralized processor using channel status information (CSI) and applied over DL or UL channels to multiplex data streams for or from multiple users. In one embodiment, the centralized processor is aware of the CSI between the distributed antenna and the client device and uses the CSI to precode data transmitted over the DL or UL channel. In the same embodiment, the CSI is estimated at the client device and returned to the distributed antenna. In another embodiment, the DL-CSI is obtained at the distributed antenna from the UL-CSI using radio frequency (RF) calibration and UL / DL channel interaction.

[0082] In one embodiment, the MU-MAS is a distributed input distributed output (DIDO) system as described in the relevant patents and applications. In another embodiment, the MU-MAS illustrated in Figure 13 consists of the following: • User equipment (UE) 1301. RF transceiver for fixed and / or mobile clients, which receives a data stream on a downlink (DL) channel from a backhaul and transmits data to the backhaul via an uplink (UL) channel. • Transmitting / receiving base station (BTS) 1302. The BTS interfaces the backhaul with a radio channel. In one embodiment, the BTS is an access point consisting of a digital-to-analog converter (DAC) / analog-to-digital converter (ADC) and a radio frequency (RF) chain that converts baseband signals to RF. In some cases, the BTS is a simple RF transceiver equipped with a power amplifier / antenna, and the RF signal is carried to the BTS by RF overfiber technology as described in the relevant patents and applications. • Controller (CTR) 1303. The CTR is a specific type of BTS designed for the following specific special functions: transmitting training signals for time / frequency synchronization of the BTS and / or UE, receiving and transmitting control information from the UE, and receiving channel status information (CSI) or channel quality information from the UE. One or more CTR stations can be included in any MU-MAS system. When multiple CTRs are available, information to and from those stations can be combined to increase diversity and improve link quality. In one embodiment, CSI is received from multiple CTRs by Maximum Ratio Combination (MRC) technique to improve CSI demodulation. In another embodiment, control information is transmitted from multiple CTRs by Maximum Ratio Transmission (MRT) to improve SNR at the receiver side. The scope of the invention is not limited to MRC or MRT, and any other diversity techniques (e.g., antenna selection) can be used to improve the radio link between the CTR and the UE. • Centralized processor (CP) 1304. The CP is a server that connects the backhaul to the internet or another type of external network 1306. In one embodiment, the CP computes MU-MAS baseband processing and transmits waveforms to the distributed BTS by DL transmission. • Base Station Network (BSN) 1305. A BSN is a network connecting a CP to a distributed BTS that carries information over either DL or UL channels. A BSN can be a wired or wireless network, or a combination of both. For example, a BSN can be a DSL, cable, fiber optic network, or a line-of-sight (LOS) or non-line-of-sight (NLO) wireless link. Furthermore, a BSN can be a unique network, a local area network, or the internet.

[0083] The following describes how the aforementioned MU-MAS framework is incorporated into the LTE standard for cellular systems (and furthermore, non-cellular systems utilizing the LTE protocol) to achieve additional gains in spectral efficiency. We begin with a general overview of the LTE framework and the modulation techniques used in DL and UL channels. Next, we provide a brief explanation of the physical layer frame structure and resource allocation in the LTE standard. Finally, we clearly describe the MU-MAS precoding methods for downlink (DL) and uplink (UL) channels in multi-user scenarios using the LTE framework. For DL ​​methods, we propose two solutions: open-loop and closed-loop DIDO methods.

[0084] LTE is designed with a flat network architecture (in contrast to the layered architecture of previous cellular standards) and offers: reduced latency, reduced packet loss through ARQ, reduced call setup time, and improved coverage and throughput through macro diversity. The network elements in the LTE network shown in Figure 6 are as follows

[79] . • GW (Gateway). This is a router that connects the LTE network to an external network (i.e., the Internet). The GW is divided into a Serving Gateway (S-GW) 601, which forms the boundary of the EUTRAN interface 608, and a PDN Gateway (P-GW) 602, which is the interface to the external network. The S-GW and P-GW are part of the so-called Evolutionary Packet Core (EPC) 609. • MME (Mobility Management Entity) 603. Manages mobility, protection parameters, and UE identity. The MME is also part of the LTE EPC. • eNodeB (Enhanced Node-B) 604: A base station that handles radio resource management, user mobility, and scheduling. UE (User Equipment) 605. This is a mobile station. • Interfaces for S1 and X2 (606 and 607). These are wired or wireless backhaul connections between the MME and eNodeB (S1-MME), between the S-GW and eNodeB (S1-U), and between multiple eNodeB (X2).

[0085] In one embodiment of the present invention, when UE is an LTE UE, the MU-MAS network is an LTE network, BTS is an LTE eNodeB, CTR is an LTE eNodeB or MME, CP is an LTE GW, and BSN is an S1 or X1 interface. Hereafter, distributed antenna, BTS, and eNodeB are used interchangeably to refer to any base station in the MU-MAS, DIDO, or LTE system.

[0086] As illustrated in Figure 7, an LTE frame has a duration of 10 milliseconds and consists of 10 subframes [33, 80]. Each subframe is divided into two slots, each with a duration of 0.5 milliseconds. The LTE standard specifies two types of frames: i) Type 1 for FDD operation, shown in Figure 7a), where all subframes are designated for either DL or UL channels; and ii) Type 2 for TDD operation, shown in Figure 7b), where some subframes are allocated to DL and some to UL (depending on the selected configuration), and some subframes are reserved for "special use." These are at least one special subframe per frame and consist of three fields: i) a downlink pilot time slot (DwPTS) reserved for DL ​​transmission; ii) a guard period (GP); and iii) an uplink pilot time slot (UpPTS) for UL transmission.

[0087] LTE uses orthogonal frequency division multiplexing (OFDM) and orthogonal frequency division multiplexing access (OFDMA) modulation for DL ​​channels, and single-carrier frequency division multiple access (SC-FDMA) for UL channels. A "resource element" (RE) is the smallest modulation structure in LTE and consists of one OFDM subcarrier in frequency and one OFDM symbol period in time, as shown in Figure 8a for DL ​​channels and in Figure 8b for UL channels. A "resource block" (RB) consists of 12 subcarriers in frequency and one 0.5-millisecond slot in time (consisting of 3 to 7 OFDM symbol periods, depending on the DL vs. UL channel and cyclic prefix type). Resource blocks for any UE are assigned on a subframe basis. Because the MU-MAS in this invention uses spatial processing to transmit multiple data streams to various UEs, all resource blocks can be assigned to the same UE in any subframe. In one embodiment, all or a subset of resource blocks are assigned to any UE, and simultaneous non-interfering data streams are transmitted to the UE via precoding.

[0088] To establish a link between the BTS and the UE, the LTE standard specifies a synchronization procedure. The BTS transmits two consecutive signals to the UE: a primary synchronization signal (P-SS) transmitted over the primary synchronization channel (PSCH) and a secondary synchronization signal (S-SS) transmitted over the secondary synchronization channel (SSCH). Both signals are used by the UE for time / frequency synchronization in addition to obtaining the cell ID. The P-SS consists of a 63-length Zadoff-Chu sequence from which the UE obtains the physical layer ID (0-2). The S-SS is an interleaved concatenation of two 31-length binary sequences used to obtain the cell ID group number (0-167). From these two identification numbers, the UE obtains the physical cell ID (PCI, defined from 0-503).

[0089] In the MU-MAS system described in this invention, there are no cell boundaries because the power transmitted from the BTS is intentionally increased to generate interference used to create a coherent region around the UE. In this invention, various BTSs are grouped into “antenna clusters” or “DIDO clusters” as defined in the relevant U.S. Patent No. 8,170,081 issued on May 1, 2012, titled “System And Method For Adjusting DIDO Interference Cancellation Based On Signal Strength Measurements”. For example, Figure 9 shows a primary antenna cluster 901 and one adjacent antenna cluster 902. Any antenna cluster consists of multiple BTSs 903.

[0090] Cell IDs can be used in MU-MAS and DIDO systems to distinguish antenna clusters. In one embodiment, the same cell ID is transmitted from all BTS in the same antenna cluster via P-SS and S-SS. In the same embodiment, different antenna clusters use different cell IDs. In another embodiment, all BTS in the same antenna cluster 1001 are grouped into “antenna subclusters” 1003 having various shaded colors as illustrated in Figure 10, and different cell IDs 1004 are associated with each antenna subcluster. In one embodiment, antenna subclusters are statistically defined according to a predetermined cluster design or GPS location information. In another embodiment, antenna subclusters are dynamically defined based on the measurement of relative signal strength between BTS or based on GPS location information. In a different embodiment of the present invention, different cell IDs are assigned to any coherence area associated with a UE (as described in the related concurrently pending U.S. Patent Application No. 13 / 232,996, titled “Systems and Methods to Exploit Areas of Coherence in Wireless Systems”).

[0091] If all BTSs within the same antenna cluster or subcluster transmit LTE broadcast channels (e.g., P-SS and S-SS) to the UE, destructive interference may degrade the performance of time or frequency synchronization enabled by the broadcast channels. Destructive interference can be caused by multipath generated from BTSs that are spaced apart and recombine non-interferentially at several UE locations. To avoid or mitigate this effect, in one embodiment of the present invention, only one of all BTS within the same antenna cluster or subcluster transmits LTE broadcast channels (e.g., P-SS and S-SS) to all UEs. In the same embodiment, the BTS transmitting the LTE broadcast channels are selected to maximize the power received by the UEs on the broadcast channels. In another embodiment, only a limited set of BTS are selected to transmit LTE broadcast channels to all UEs simultaneously so that destructive interference is avoided at the UEs. In different embodiments of the present invention, the LTE broadcast channels are transmitted at a power higher than the payload to reach all UEs within the same antenna cluster or subcluster.

[0092] As described above, LTE-Advanced supports carrier aggregation (CA) to improve data rates on DL channels. In MU-MAS, CA can be used in combination with precoding to increase the per-user data rate. In one embodiment of this invention, transmission precoding is applied to different parts of the RS spectrum (interband CA) or different bands within the same spectrum (intraband CA) to increase the per-user data rate. When using interband CA, path loss in different bands can vary significantly because those bands are centered at different carrier frequencies. In conventional LTE cellular systems, frequency bands at low carrier frequencies may experience lower path loss than those at high carrier frequencies. Therefore, applying interband CA to a cellular system can cause undesirable inter-cell interference at low carrier frequencies. In contrast, the MU-MAS of this invention is not limited by interference at cell boundaries because the BTS is distributed and the concept of cells does not exist. This more flexible system layout enables various methods of interband CA in MU-MAS. In one embodiment of the present invention, the MU-MAS enables interband CA by operating one set of BTS at a lower carrier frequency and another set of BTS at a higher carrier frequency, so that the two sets intersect or one set is a subset of the other. In another embodiment, the MU-MAS with precoding uses the CA method in conjunction with a frequency hopping pattern to improve robustness against frequency-selective fading or interference.

[0093] 1. Downlink Closed-Loop MU-MAS Precoding Method in LTE The MU-MAS closed-loop scheme can be used with either time-division duplex (TDD) or frequency-division duplex (FDD) systems. In FDD systems, the DL and UL channels operate at different frequencies. Therefore, DL channel status information (CSI) must be estimated on the UE side and reported back to the CP via the UL channel through the BTS or CTR. In TDD systems, the DL and UL channels are set to the same frequency, and the system may use either closed-loop or open-loop techniques, taking advantage of channel reciprocity (as described in the following sections). The main disadvantage of closed-loop techniques is that they require feedback, which introduces greater overhead for control information on the UL.

[0094] The general mechanism for the closed-loop scheme in MU-MAS is as follows: i) The BTS transmits signaling information to the UE over the DL; ii) The UE uses this signaling information to estimate the DL CSI from all "active BTS"; iii) The UE quantizes the DL CSI or uses the codebook to select precoding weights to be used in the next transmission; iv) The UE transmits the quantized CSI or codebook index to the BTS or CTR over the UL channel; v) The BTS or CTR reports the CSI information or codebook index to the CP, which calculates the precoding weights for the data transmission over the DL. An "active BTS" is defined as a set of BTSs reachable by a given UE. For example, in related concurrently pending U.S. Patent Application No. 12 / 802,974, titled "System And Method For Managing Inter-Cluster Handoff Of Clients Which Traverse Multiple DIDO Clusters," and related concurrently pending U.S. Patent Application No. 12 / 917,257, titled "Systems And Methods To Coordinate Transmissions In Distributed Wireless Systems Via User Clustering," a "user cluster" 905 is defined as a set of BTS reachable by a given UE, as illustrated in Figure 9. The number of active BTS is limited to user clusters to reduce the amount of CSI estimated from the BTS to a given UE, thereby reducing feedback overhead on the UL and the complexity of MU-MAS precoding calculations in the CP.

[0095] As described in paragraph

[0083] , MU-MAS precoding uses either a linear or nonlinear method. In the case of a nonlinear method (e.g., dirty paper coding [68-70]) or Tomlison-Harashima precoding [71-72], grid techniques or trellis precoding [73-74], vector perturbation techniques [75-76]), continuous interference cancellation is applied at the transmitter to avoid inter-user interference. In this case, the precoding matrix is ​​calculated to explain the CSI to all UEs in the antenna cluster. Alternatively, a linear precoding method (e.g., zero-forcing

[65] , block diagonalization [66-67], matrix inversion, etc.) can be used on a user cluster basis so that the precoding weights for each UE are calculated independently of other UEs. Depending on the number of UEs and eNodeBs in the antenna cluster and user cluster, the linear versus nonlinear precoding method provides a range of computational performance. For example, if MU-MAS consists of K UEs per antenna cluster, M eNodeBs per antenna cluster, and C eNodeBs per user cluster, the complexity of linear precoding is O(K). * C 3 ) on the other hand, for nonlinear precoding it is O(M * K 2Therefore, it is desirable to develop a method to reduce the computational complexity at the CP by dynamically switching between two types of precoding techniques based on the number of UEs and eNodeBs in the MU-MAS. In one embodiment of the present invention, the MU-MAS uses a linear precoding method. In another embodiment, the MU-MAS uses a nonlinear precoding method. In the same embodiment of the present invention, the MU-MAS dynamically switches between linear and nonlinear precoding methods based on the number of UEs and eNodeBs in the antenna cluster and user cluster to reduce the computational complexity at the CP. In a different embodiment, the MU-MAS switches between a precoding multiplexing method for UEs experiencing good channel quality (e.g., near the eNodeB) and a beamforming or diversity method for UEs with poor link quality (e.g., far from the eNodeB).

[0096] 1.1 Downlink MU-MAS signaling method within the LTE standard The LTE standard defines two types of reference signals (RS) that can be used for closed-loop DL signaling [33, 50, 82-83]: i) cell-specific reference signals (CRS), and ii) UE-specific RS, such as channel status information (CSI-RS) and demodulated RS (DM-RS). Cell-specific RS are not precoded, but UE-specific RS are

[50] . CRS is used in LTE Release 8, which uses SU / MU-MIMO codebook-based technology where each cell uses up to four antennas. LTE-Advanced Release 10 supports non-codebook-based SU / MU-MIMO schemes with up to eight transmit antennas, and CoMP schemes where antennas are distributed across different cells. Thus, Release 10 enables more flexible signaling schemes with CSI-RS. In this invention, we describe how each type of signaling scheme can be used in a MU-MAS system to enable precoding.

[0097] 1.1.1 MU-MAS signaling using CRS CRS is used in LTE (Release 8) systems to estimate the CSI from all transmitting antennas to the UE in the BTS [80, 84]. CRS is obtained as the product of a two-dimensional orthogonal sequence and a two-dimensional pseudo-random (PRN) sequence. For a total of 504 different CRS sequences, there are three orthogonal sequences (i.e., placed on top of an orthogonal set of OFDM subcarriers) and 168 possible PRN sequences. Each sequence uniquely identifies one cell. Each of the three orthogonal CRSs is associated with one of three physical layer IDs (0-2) that generate different cell IDs, as described in the previous subsection. CRS is transmitted in the first and third to last OFDM symbols of all slots, as well as in every sixth subcarrier. The orthogonal patterns of time and frequency are designed for each transmitting antenna in the BTS so that the UE can uniquely estimate the CSI from each of the transmitting antennas. Release 8 specifies up to four orthogonal patterns per CRS, one for each of the four transmitting antennas used in MIMO 4x4. This high-density CRS in terms of time and frequency (i.e., transmitted for every 0.5 millisecond slot and every sixth subcarrier) generates a 5% overhead and is intentionally designed to support scenarios with fast channel variations in terms of time and frequency

[83] .

[0098] In Release 8, there are up to three orthogonal CRSs with four orthogonal patterns for each multi-antenna mode (or six orthogonal CRSs for single-antenna mode), so that up to 12 transmitting antennas can be distinguished within the same coverage region without causing interference to the CRS. In one embodiment of the present invention, antenna cluster 1001 is divided into three antenna subclusters 1005 as shown in Figure 10. Different physical layer IDs (or cell IDs) are associated with each antenna subcluster, and each antenna subcluster is assigned to one of three orthogonal CRSs with four orthogonal patterns (i.e., each antenna subcluster can support up to four BTS without causing interference to the CRS from other BTS). In this embodiment, any cluster can support up to 12 BTS without causing interference to the CRS.

[0099] In scenarios where more than 12 BTS are located within the same cluster, it is desirable to increase the number of available orthogonal CRSs (i.e., BTS that simultaneously transmit precoded signals to the UE) that support a larger number of active BTS. One way to achieve this is to define more than three antenna subclusters 1003 for each antenna cluster 1101 and assign the same three physical layer IDs (or cell IDs 0-2 1104) to the antenna subclusters 1103 having a repeating pattern as shown in Figure 11. Antenna subclusters have been observed to be obtained in various ways, defined in such a way that no user cluster 1102 can reach two antenna subclusters with the same physical layer ID, thereby avoiding interference with the CRS. For example, one way to achieve this is to define an area of ​​antenna subcluster 1103 larger than the user cluster 1102, ensuring that its adjacent antenna subclusters do not use the same physical layer ID. In one embodiment of the present invention, multiple antenna subclusters are arranged within the same antenna cluster in a repeating pattern so that the corresponding CRSs do not interfere with each other, thereby enabling non-interference simultaneous transmission from more than 12 BTSs.

[0100] In a real MU-MAS system, every UE may allow more than four BTS within its user cluster. For example, Figure 12 shows the SNR distribution for a real-world deployment of a DIDO or MU-MAS system in the urban area of ​​San Francisco, California. The propagation model is based on the 3GPP path loss / shadowing model

[81] and assumes a carrier frequency of 900 MHz. The dots on the map indicate the locations of DIDO-BTS, while the black circles indicate user clusters (UEs are located at the center of the circles). In sparsely populated areas 1201, UEs may allow only two or three BTS within their user cluster (for example, only three BTS in the example in Figure 12), while in densely populated areas 1202, each user cluster can contain as many as 26 BTS, as shown in Figure 12.

[0101] The high redundancy of CRS can be utilized in MU-MAS to enable CSI estimation from any number of transmitting antennas greater than four. For example, if the channel is fixed radio or characterized by a low Doppler effect, it is not necessary to calculate the CSI from all four transmitting antennas every 0.5 milliseconds (slot duration). Similarly, if the channel is frequency flat, estimating the CSI for each sixth subcarrier is redundant. In this case, the resource elements (REs) occupied by the redundant CRS can be reallocated to another transmitting antenna or BTS in the MU-MAS. In one embodiment of the present invention, the system allocates the resource elements of the redundant CRS to an extra antenna or BTS in the MU-MAS system. In another embodiment, the system estimates the time and frequency selectivity of the channel and dynamically allocates CRSs for different BTSs or only BTS within a user cluster to different resource elements.

[0102] The number of BTSs in any user cluster depends on the signal output level from all BTS in the user cluster, as measured by the UE, relative to the noise output level or signal-to-noise ratio (SNR). In one embodiment, the UE estimates the SNR from all neighboring BTS and selects the BTS belonging to its user cluster based on the SNR information. In another embodiment, the CP recognizes the SNR from each BTS to the UE (based on feedback information from the UE or information obtained from the UL channel by inferring UL / DL channel interoperability) and selects a set of BTS to be included in any user cluster.

[0103] The number of BTSs included in each user cluster determines the performance of the MU-MAS method described in the present invention. For example, if the number of BTSs per user cluster is low, the UE will experience a higher level of out-of-cluster interference, resulting in a high signal-to-interference plus noise power ratio (SINR) and a low data rate. Similarly, if a large number of BTSs are selected for each user cluster, the SNR from the BTS measured at the edge of the user cluster by the UE will be low and may be affected by out-of-cluster interference from adjacent BTS outside the user cluster. There is an optimal number of BTSs per user cluster that yields the highest SINR and data rate. In one embodiment of the present invention, the CP selects the optimal number of BTS per user cluster to maximize the SINR and data rate to the UE. In another embodiment of the present invention, the BTS per user cluster are dynamically selected to adapt to changing conditions of the propagation environment or UE mobility.

[0104] Another drawback of using a large number of BTS per user cluster is its high computational load. In practice, more BTS per user cluster increases the computational complexity of the MU-MAS precoder. In one embodiment, the number of BTS per user cluster is selected to obtain an optimal trade-off between SINR or data rate performance and the computational complexity of the MU-MAS precoder. In another embodiment, the number of BTS per user cluster is dynamically selected based on a trade-off between propagation conditions and the computational resources available in the MU-MAS.

[0105] 1.1.2 MU-MAS signaling using CSI-RS and DM-RS In the LTE-Advanced (Release 10) standard, CSI-RS is used by any UE to estimate the CSI from a BTS [33, 83]. The standard defines orthogonal CSI-RS for different transmitters in a BTS, allowing UEs to distinguish CSIs from different BTSs. Up to eight transmitting antennas in a BTS are supported by CSI-RS, as shown in Table 6.10.5.2-1, 2 of

[33] . CSI-RS is transmitted with periodicity over 5 to 80 subframes (i.e., CSI-RS is transmitted every 5 to 80 milliseconds), as shown in Table 6.10.5.3-1 of

[33] . The periodicity of the LTE-Advanced CSI-RS is deliberately designed to be larger than that of the LTE CRS, especially for older LTE terminals that cannot use these extra resources, in order to avoid excessive overhead of control information. Another reference signal used for CSI estimation is demodulated RS (DM-RS). DM-RS is a demodulation reference signal intended for a specific UE, and is simply transmitted within a resource block allocated for transmission to that UE.

[0106] When there are more than eight antennas (the maximum number of transmitters supported by the LTE-Advanced standard) in a user cluster, alternative techniques must be used to enable DIDO precoding while maintaining system compliance with the LTE-Advanced standard. In one embodiment of the invention, each UE uses CSI-RS, DM-RS, or a combination of both to estimate the CSI from all active BTS in its own user cluster. In the same embodiment, the DIDO system detects the number of BTS in the user cluster and whether the user cluster complies with the LTE-Advanced standard (which supports up to eight antennas). If it does not comply, the DIDO system uses alternative techniques to enable DL signaling from the BTS to the current UE. In one embodiment, the transmit power from the BTS is reduced until up to eight BTS are reachable by the UEs in that user cluster. However, this solution may result in a reduction in data rate because it reduces coverage.

[0107] Another solution is to divide the BTS within the user cluster into subsets and send a set of CSI-RS for all subsets simultaneously. For example, if the periodicity of the CSI-RS is five subframes (i.e., 5 milliseconds) as shown in Table 6.10.5.3-1 of

[33] , then every 5 milliseconds, the CSI-RS will be sent from a new subset of the BTS. Note that this solution works as long as the CSI-RS periodicity is short enough to span all BTS subsets within the UE's channel coherence time (which is a function of the UE's Doppler velocity). For example, if the selected CSI-RS periodicity is 5 milliseconds and the channel coherence time is 100 milliseconds, it is possible to define up to 20 subsets of 8 BTS each, while adding a total of 160 BTS in the user cluster. In another embodiment of the invention, the DIDO system estimates the channel coherence time of the UE and determines how many BTS can be supported within the user cluster to avoid degradation due to channel fluctuations and Doppler effects with respect to a given CSI-RS periodicity.

[0108] All proposed solutions for CSI-RS so far comply with the LTE standard and can be deployed within the framework of conventional LTE systems. For example, a proposed method enabling more than eight antennas per user cluster requires no modification to the UE LTE hardware and software implementation, and only minor modifications to the protocols used in the BTS and CP to allow for the selection of BTS subsets at any time. These modifications can be easily implemented on a cloud-based software-defined radio (SDR) platform, which is one promising deployment paradigm for DIDO and MU-MAS systems. Alternatively, if it is possible to relax the constraints of the LTE standard and develop slightly modified hardware and software for the LTE UE to support LTE-like but non-LTE-compliant DIDO or MU-MAS operating modes, the UE can operate in either a fully LTE-compliant mode or a modified mode that supports non-LTE-compliant DIDO or MU-MAS operation. For example, this would allow for another solution to increase the number of CSI-RS to enable a larger number of BTS in the system. In another embodiment of the invention, different CSI-RS patterns and periodicities are possible as means of increasing the number of BTS supported per user cluster. Since such minor modifications to the LTE standard may be small enough, existing LTE UE chipsets can be used simply by software modifications. Or, even if hardware modifications are required for the chipset, the changes would be small.

[0109] 1.2 Uplink MU-MAS CSI Feedback Method within the LTE Standard In the LTE and LTE-Advanced standards, the UE feeds information back to the BTS to communicate its current channel status and precoding weights for closed-loop transmissions on DL channels. Three different channel indices are included in those standards.

[35] • Rank Index (RI): Indicates how many spatial streams are transmitted to a given UE. This number is always equal to or less than the number of transmitting antennas. • Precoding Matrix Index (PMI): An index of codebooks used for precoding on DL channels. • Channel Quality Index (CQI): Defines the modulation and forward error correction (FEC) coding scheme used on the DL to maintain a defined error rate performance for a given channel condition.

[0110] While only one RI is reported for the entire bandwidth, PMI and CQI reports can be broadband or subband-based, depending on the channel's frequency selectivity. These indices are transmitted in the UL over two different types of physical channels: i) a physical uplink control channel (PUCCH) used solely for control information, and ii) a physical uplink shared channel (PUSCH) used for both data and control information, allocated on a single resource block (RB) and on a subframe basis. For PUCCH, the procedure for reporting RI, PMI, and CQI is periodic, and the indices can be broadband (for frequency-flat channels) or subband-based and selected per UE (for frequency-selective channels). For PUSCH, the feedback procedure is aperiodic and can be subband-based (for frequency-selective channels) or on a higher-layer configured subband (e.g., for LTE-Advance transmission mode 9 with eight transmitters) and selected per UE.

[0111] In one embodiment of the invention, the DIDO or MU-MAS system uses RI, PMI, and CQI to report the current channel status and precoding information to the BTS and CP. In one embodiment, the UE uses the PUCCH channel to report these indicators to the CP. In another embodiment, if more indicators are required for DIDO precoding, the UE uses PUSCH to report additional indicators to the CP. If the channel is frequency flat, the UE can utilize extra UL resources to report PMI for more antennas in the DIDO system. In one embodiment of the invention, the UE or BTS or CP estimates the channel frequency selectivity, and if the channel is frequency flat, the UE utilizes extra UL resources to report PMI for more BTS.

[0112] 2. Downlink Open-Loop MU-MAS Precoding Method in LTE The open-loop MU-MAS precoding scheme can only be used in time-division duplex (TDD) systems that utilize RF calibration and channel interoperability. The general mechanism of the open-loop scheme in MU-MAS consists of the following: i) UEs transmit signaling information to the BTS or CTR over the UL; ii) the BTS or CTR uses this signaling information to estimate UL CSI from all UEs; iii) the BTS or CTR converts the UL CSI to DL CSI using RF calibration; iv) the BTS or CTR transmits the DL CSI or codebook index to the CP via the BSN; v) based on the DL CSI, the CP calculates precoding weights for data transmission over the DL. Similar to the closed-loop MU-MAS precoding scheme, the user cluster can be used to reduce the amount of CSI from UEs estimated in the BTS, thereby reducing the computational burden in the BTS and the amount of signaling required on the UL. In one embodiment of the present invention, the open-loop precoding technique is used to transmit a simultaneous non-interfering data stream from the BTS to the UE over the DL channel.

[0113] In LTE, there are two types of reference signals for uplink channels [31,33,87]: i) a sounding reference signal (SRS) used for scheduling and link application, and ii) a demodulation reference signal (DMRS) used for data reception. In one embodiment of the present invention, the DMR is used in an open-loop precoding system to estimate the UL channel from all UEs to all BTSs. In the time domain, the DMRS is transmitted in the fourth OFDM symbol (when using a typical cyclic prefix) for all LTE slots (with a duration of 0.5 milliseconds). In the frequency domain, the DMRS transmitted over the PUSCH is mapped for all UEs to the same resource block (RB) used by that UE for UL data transmission. The length of the DMRS is M RS =mN RB Here, m is the number of RBs, and N RB=12 is the number of subcarriers per RB. To support multiple UEs, up to 12 DMRSs can be generated from a single basic Zadoff-Chu

[88] or computer-generated constant amplitude zero autocorrelation (CG-CAZAC) sequence by 12 possible cyclic shifts of the basic sequence. The basic sequence is divided into 30 groups, and neighboring LTE cells select DMRSs from different groups to reduce inter-cell interference. For example, if the maximum number of resource blocks in a single OFDM symbol is 110 (i.e., assuming an overall signal bandwidth of 20 MHz), it is possible to generate up to 110 × 30 = 3300 different sequences. The 30 basic sequences are not guaranteed to be orthogonal and are observed to be designed to reduce, rather than completely eliminate, interference across cells. In contrast, the 12 cyclic shifts of the same basic sequence are orthogonal, thereby enabling up to 12 UEs to be transmitted UL on the same RB without interference. The value of the cyclic shift used by any UE is provided by the BTS through Downlink Control Information (DCI) messages transmitted via the PDCCH. In Release 8, the DCI consists of 3 bits, which limits the UE to using only 8 cyclic shifts in a pool of 12 possible choices.

[0114] The cyclic shift of the basic DMRS sequence is used in this invention to enable the use of MU-MIMO on UL channels and to allow the estimation of CIS from multiple UEs for DL ​​precoding when channel interoperability is utilized in TDD mode. In one embodiment of the invention, the open-loop precoding method is used to transmit a simultaneous non-interfering data stream from a distributed BTS to a UE on a DL channel. In a different embodiment of the invention, the open-loop MU-MIMO method is used to receive a simultaneous non-interfering data stream from a UE to a BTS on a UL channel. The same CSI estimated from all active UEs on the UL can be used to calculate a receive space filter for MU-MIMO operation, in addition to the DL precoding weights. Because Release 8 only specifies up to eight orthogonal DMRS (by the limited DCI bits as described above), the MU-MIMO method for UL channels and the MU-MAS precoding method for DL ​​channels can support up to eight UEs, assuming that all UEs utilize the full UL bandwidth.

[0115] One way to increase the number of UEs that can be simultaneously addressed through MU-MIMO in UL or MU-MAS precoding in DL is to multiplex the UE's DMRS on the frequency domain. For example, when a 10 MHz bandwidth is used in TDD mode, there are 50 RBs that can be assigned to UEs. In this case, 25 interleaved RBs can be assigned to one group of eight UEs, and the remaining 25 interleaved RBs can be assigned to another group of UEs, for a total of 16 UEs that can be simultaneously addressed. The CSI is then calculated by interpolating the estimation from the DMRS transmitted on the interleaved RBs. A larger number of simultaneously addressed UEs can be supported by increasing the number of interleaved patterns of the UL RBs. These patterns can be statically or dynamically assigned to different UEs by a specific frequency-hopping sequence. In one embodiment of the present invention, to increase the number of UEs supported through MU-MIMO or MU-MAS precoding, the DMRS are assigned to UEs on orthogonal interleaved RBs. In the same embodiment, the interleaved RBs are assigned statically. In another embodiment, interleaved RBs are dynamically assigned by a specific frequency hopping pattern.

[0116] An alternative solution is to multiplex the DMRS for different UEs in the time domain. For example, UEs are divided into different groups, and the DMRS for those groups are transmitted over consecutive time slots (each with a duration of 0.5 milliseconds). However, in this case, it is necessary to ensure that the periodicity of the DMRS assignments for different groups is lower than the channel coherence time of the fastest moving UE. In fact, this is a requirement to ensure that the channel does not change for all UEs from the time the CSI estimates it to be based on the DMRS until the time the system transmits the DL data stream to the UEs via DIDO precoding. In one embodiment, the system divides the active UEs into groups and assigns the same set of DMRs to each group over consecutive time slots. In the same embodiment, the system estimates the shortest channel coherence time for all active UEs, as well as the maximum number of UE groups and the periodicity of the time multiplexing of the DMRS based on that information.

[0117] Another solution is to spatially separate different groups of UEs that use the same set of DMRSs. For example, the same set of orthogonal DMRSs can be used for all UEs from different antenna subclusters in Figure 11, identified by the same cell ID. In one embodiment of the present invention, groups of UEs using the same set of orthogonal DMRSs are spatially separated to avoid interference between groups. In the same embodiment, the same set of orthogonal DMRSs is used by different antenna subclusters identified by the same cell ID. The MU-MAS may assign UEs to “virtual cells” to maximize the number of DMRSs that can be used in the UL. In one exemplary embodiment, a virtual cell is a coherence area around a UE (as described in the related concurrently pending U.S. Patent Application No. 13 / 232,996, titled “Systems and Methods to Exploit Areas of Coherence in Wireless Systems”), and the DIDO system generates up to 3300 coherence areas with respect to different UEs. In another embodiment of the present invention, each of the 30 basic sequences is assigned to a different antenna cluster in order to reduce inter-cluster interference between adjacent antenna clusters (clusters as defined in the relevant U.S. Patent No. 8,170,081 issued May 1, 2012, titled "System And Method For Adjusting DIDO Interference Cancellation Based On Signal Strength Measurements").

[0118] 3. Uplink MU-MAS method in LTE Embodiments of the present invention use an open-loop MU-MIMO scheme on a UL channel to receive simultaneous UL data streams from all UEs to a BTS. The UL open-loop MU-MIMO scheme consists of the following steps: i) the UEs transmit signaling information and data payloads to all BTSs; ii) the BTS uses the signaling information to calculate channel estimations from all UEs; iii) the BTS transmits the channel estimations and data payloads to a CP; iv) the CP uses the channel estimations to remove inter-channel interference from the data payloads of all UEs via spatial filtering and demodulates the data streams from all UEs. In one embodiment, the open-loop MU-MIMO system uses single-carrier frequency-division multiplexing (SC-FDMA) to increase the number of UL channels from the UEs to the BTS and multiplexes them in the frequency domain.

[0119] In one embodiment, synchronization between UEs is achieved by signaling from the DL, either by direct wiring to the same clock or, in one embodiment by GPSDO, by sharing a common time / frequency reference, with all BTSs considered locked to the same time / frequency reference clock. Variations in channel delay across different UEs can generate jitter between the time references of different UEs, potentially affecting the performance of the MU-MIMO method on the UL. In one embodiment, to reduce relative propagation delay across different UEs, only UEs in the same antenna cluster (e.g., adjacent UEs) are processed by the MU-MIMO method. In another embodiment, relative propagation delay between UEs is compensated in the UE or in the BTS, with the BTS ensuring simultaneous reception of data payloads from different UEs.

[0120] The method for enabling signaling information regarding data demodulation on the UL is the same method used for signaling in the downlink open-loop DIDO scheme described in a previous section. The CP uses different spatial processing techniques to remove inter-channel interference from the UE data payload. In one embodiment, the CP uses a nonlinear spatial processing method such as a maximum likelihood (ML), decision feedback equalization (DFE), or successive interference rejection (SIC) receiver. In another embodiment, the CP demodulates the uplink data streams individually, using a linear filter such as a zero-forcing (ZF) or least mean squares error (MMSE) receiver to cancel out same-channel interference.

[0121] 4. Integration with existing LTE networks In the United States and other parts of the world, LTE networks are already operational, where they are being deployed, and / or are scheduled to be deployed. It would be of significant benefit to LTE operators if they could gradually deploy DIDO or MU-MAS capabilities into their existing or already-promised deployments. In this way, they can deploy DIDO or MU-MAS in the areas where it provides the most immediate benefits, and gradually expand DIDO or MU-MAS capabilities to extend across more networks. Eventually, once they have sufficient DIDO or MU-MAS coverage in their areas, they can choose to completely decommission cells and, instead, switch entirely to DIDO or MU-MAS to achieve much higher spectrum density at a very low cost. Through this complete transition from cellular to DIDO or MU-MAS, LTE operators' radio customers will never suffer any loss of service. Rather, they will simply experience improvements in the throughput and reliability of their data, while operators will experience cost reductions.

[0122] There are several embodiments that enable the gradual integration of DIDO or MU-MAS into existing LTE networks. In all cases, the BTS for DIDO or MU-MAS will be called a DIDO-LTE BTS, and it will utilize one of the LTE-compatible DIDO or MU-MAS embodiments described above, or other LTE-compatible embodiments that may be developed in the future. Alternatively, the DIDO-LTE BTS will utilize a minor modification of the LTE standard as described above, and the UE will either be updated (for example, if a software update is sufficient to modify the UE to be compatible with DIDO or MU-MAS), or a new generation of UE that is DIDO or MU-MAS compatible will be deployed. In either case, the new BTS supporting DIDO or MU-MAS, whether within the constraints of the LTE standard or as a modification of the LTE standard, will hereafter be referred to as a DIDO-LTE BTS.

[0123] The LTE standard supports various channel bandwidths (e.g., 1.4, 3, 5, 10, 15, and 20 MHz). In one embodiment, an operator of an existing LTE network would support conventional LTE BTS in a cellular configuration on one block of spectrum and DIDO LTE BTS on another block of spectrum, either by allocating new bandwidth for LTE-DIDO BTS or by subdividing the existing LTE spectrum (e.g., 20 MHz could be subdivided into two 10 MHz blocks). In effect, this would establish two separate LTE networks, and UE devices would be configured to use one or the other network, or to choose between the two. In the case of a subdivided spectrum, the spectrum would be divided uniformly or unevenly between the conventional LTE network and the DIDO-LTE BTS network, and more spectrum could be allocated to the network that is most readily available, taking into account the degree of deployment of cellular LTE BTS and DIDO-LTE BTS, and / or patterns of UE usage. This subdivision can change as needed over time, and at some point, when there are enough DIDO-LTE BTS deployed to provide the same or better coverage as cellular BTS, the entire spectrum can be allocated to DIDO-LTE BTS and the cellular BTS can be decommissioned.

[0124] In another embodiment, conventional cellular LTE BTS can be configured to cooperate with DIDO-LTE BTS, sharing the same spectrum but alternating its use. For example, if they share spectrum usage equally, each BTS network would alternately utilize one 10-millisecond frame time, for example, one 10-millisecond frame for the cellular LTE BTS followed by one 10-millisecond frame for the DIDO-LTE BTS. The frame times can also be subdivided into non-uniform intervals. This subdivision can change as needed over time, and when there are enough DIDO-LTE BTS deployed to provide the same or better coverage as the cellular BTS, all the time can be allocated to the DIDO-LTE BTS and the cellular BTS can be decommissioned.

[0125] In another embodiment of the present invention, DIDO or MU-MAS is used as LOS or NLOS radio backhaul to small cells in LTE and LTE-Advanced networks. As small cells are deployed in the LTE network, DIDO or MU-MAS provides high-speed radio backhaul to those small cells. As the demand for higher data rates increases, more small cells are added to the network until a limit is reached in which the radio network cannot add any more small cells to a given area without causing inter-cell interference. In the same embodiment of the present invention, DIDO-LTE BTS is used to gradually replace small cells, thereby leveraging inter-cell interference to provide increased network capacity.

[0126] 5. MU-MAS LTE Scheduler In MU-MAS, distributed antennas or BTS transmit simultaneous precoded data streams to multiple UEs. As described in the relevant patents and applications, the number of BTSs must be equal to or greater than the number of UEs to enable simultaneous data transmission. In actual deployments, the number of UEs may exceed the number of BTSs. In this case, the excess UEs can be selected to transmit in different time slots or frequency bands according to a specific scheduling policy. The scheduler utilizes channel quality information of the UEs to determine the best pair of UEs to correspond in terms of delivery time and frequency. Different scheduling methods are used in this invention, including proportional fair schedulers, round-robin, or greedy methods.

[0127] As described in the previous section, the LTE standard specifies two parameters that inform the scheduler about the link quality of any UE: CQI and SRS. CQI measures the quality of the DL channel and is supplied from the UE to the BTS and returned. SRS is signaling information transmitted from the UE to the BTS for measuring the UL channel quality. Both metrics provide information on UL / DL channel quality over time and in the frequency domain. Since DL and UL channel quality can vary with different carrier frequencies, the DL scheduler in an FDD system must use CQI as a performance measure. In TDD mode, DL scheduling uses either CQI or SRS or a combination of both to make scheduling decisions. Similar performance metrics can also be used for UL scheduling. In one embodiment of the present invention, the MU-MAS scheduler uses CQI and SRS as performance metrics used by the scheduling algorithm.

[0128] The MU-MAS described in the present invention makes available one additional channel quality metric not disclosed in the prior art: the spatial selectivity index (SSI) described in related U.S. Patent Application No. 13 / 475,598, titled "Systems and Methods to enhance spatial diversity in distributed-input distributed-output wireless systems." The SSI can be calculated based on the CIS obtained from all UEs via a feedback mechanism, or from UL channels (by applying UL / DL channel interoperability). In one embodiment of the present invention, the scheduler uses the SSI as a performance metric. The SSI is a measure of the spatial diversity available in the wireless link. The SSI depends on the spatial characteristics of the BTS in addition to the UEs. In one exemplary embodiment of the present invention, the scheduler obtains the SSI from all UEs and schedules the UEs with the "optimal" SSI according to a specific scheduling criterion. If more BTSs are available than active BTSs, the user selection criteria described above are combined with the antenna selection method described in related U.S. Patent Application No. 13 / 475,598, titled "Systems and Methods to enhance spatial diversity in distributed-input distributed-output wireless systems." In one embodiment of the present invention, the scheduler selects an optimal subset of BTSs and UEs based on specific scheduling criteria.

[0129] Referring to Figures 9, 10, and 11, in certain scenarios, the orthogonal signaling sequence may not be sufficient to allow a large number of BTSs within the same antenna cluster or subcluster. In this case, some degree of interference may occur when additional BTSs are activated to cover areas with a larger number of active UEs. In one embodiment of the present invention, the scheduler measures the degree of interference between antenna clusters or subclusters and schedules UEs to minimize the effect of that interference on the radio link.

[0130] The antenna selection algorithm described in related U.S. Patent Application No. 13 / 475,598, titled "Systems and Methods to enhance spatial diversity in distributed-input distributed-output wireless systems," is used in the present invention to select the optimal set of active BTSs based on SSI. However, this antenna selection algorithm can require high computational complexity because it must be applied to permutations of all possible antenna subsets before the MU-MAS precoding process makes a determination about the best subset based on the SSI performance metric. In MU-MAS systems with a large number of cooperative BTSs, this computational load may be expensive or impractical in actual deployments. Therefore, it is desirable to develop an alternative method that reduces the number of antenna subsets while maintaining good performance of the antenna selection method. In one embodiment of the present invention, the MU-MAS uses a method, hereafter referred to as the "antenna shuffling method," based on a queue of antenna subset ID numbers. In one embodiment of the present invention, the antenna shuffling method subdivides a queue containing all possible antenna subset IDs (i.e., all possible permutations of active BTS for a given set of available BTS) into various groups and assigns different priorities to these groups. These groups are defined to assign a fair chance to all selected subset IDs, but the SSI metric is calculated for only a limited number of subsets (e.g., the highest priority ones), thus reducing the complexity of the calculation. In one exemplary embodiment, the queue of subset IDs is divided into three groups, each assigned a different rule: i) Group 1 contains the highest priority IDs, which are only pulled from the group when a new subset with a higher priority is identified; ii) Group 2 contains new antenna subsets (selected from Group 3) in every iteration of the method; and iii) Group 3 contains antenna subset IDs that are shuffled according to a round-robin rule.Subset IDs within groups 1 and 2 are classified based on their priority in each iteration of the method, and subset IDs from group 2 are given the opportunity to be upgraded to group 1. The SSI is calculated only for subsets within groups 1 and 2, and the antenna selection algorithm is applied only to these subsets.

[0131] 6. MU-MAS LTE User Equipment The present invention includes various designs for LTE UEs. In one embodiment, the UE is an LTE UE compatible with MU-MAS using precoding, as previously described and illustrated in Figure 13.

[0132] In a different embodiment, as shown in Figure 14, the UE 1401 is connected to different devices 1402 and 1403 through a first network interface 1404 (e.g., Wi-Fi, USB, Ethernet®, Bluetooth®, optical fiber, etc.) and to the MU-MAS through a second network interface 1405. The UE in Figure 14 implements two different network interfaces, each network interface having one or more antennas (however, in an alternative embodiment, the first network interface 1404 may be a wired interface without antennas). The antennas of the first network interface are indicated by circles, and the antennas of the second network interface are indicated by triangles. In the same embodiment, the second network interface supports MU-MAS precoding, MU-MAS implementing an LTE-compliant protocol, or MU-MAS (with or without LTE-compliant protocol implementation) and an alternative network. In the same embodiment, the alternative network is a cellular network, an LTE network, or a Wi-Fi network. In the same embodiment, the UE operates with one and / or both MU-MAS and / or an alternative network, and the UE selects one of the MU-MAS or alternative network based on some criteria. In the same embodiment, the criteria are i) whether only one network is available and selected, ii) whether one network has better performance, iii) whether one network is more economical, iv) whether one network is less congested, or v) whether one network uses fewer UE resources.

[0133] In one embodiment of the present invention, the UE 1501 is housed in a case that is physically mounted on the user device 1502, as shown in Figure 15. In the same embodiment, the case serves as a decorative addition to the user device. In another embodiment, the case serves to protect the user device from physical damage. The UE consists of a battery 1503 and one or more network interfaces 1504.

[0134] In one embodiment, the UE electronic device is housed within a case. In the same embodiment, the UE electronic device includes a battery 1503. The battery includes a power charger connected via physical electrical contact or wireless contact. Exemplary power connections are conductive, dielectric, RF, optical, or thermal, but power connections are not limited to these methods. In the same embodiment, the UE electronic device is connected to receive power from a user device. This power connection is via physical contact, or via dielectric or wireless contact. In the same embodiment, the user device is connected to receive power from a MU-MAS UE. This connection is via physical contact, or via dielectric or wireless contact. In different embodiments, the same power charger powers both the user device and the MU-MAS UE.

[0135] In one embodiment of the present invention, the UE is configured to communicate with a user device. In the same embodiment, the UE is resettable (for example, via a switch or by removing power) so that the user device can initially connect to the UE, and once the connection is established, the UE is configurable by the user device. Such configuration includes configuring a private password and / or other security protocols. In a different embodiment, the UE includes means for which it is configured to communicate with the user device. Such configuration is done via a communication port which is a USB to another device, or via controls and / or buttons on the UE, or via a display which uses buttons or touch input.

[0136] In another embodiment, the same RF chain is used for MU-MAS communication in addition to the alternative network. In yet another embodiment, different RF chains are used for MU-MAS communication and the alternative network.

[0137] "References" [1]A.Paulraj,R.Nabar,and D.Gore,Introduction to Space-Time Wireless Communications,Cambridge University Press,40 West 20th Street,New York,NY,USA,2003

[0138] [2]D.Gesbert,M.Shafi,D.Shiu,P.J.Smith and A.Naguib,「From theory to practice:an overview of MIMO space-time coded wireless systems」,IEEE Journal on Selected Areas on Communications,vol.2,n.3,pp.281~302,Apr.2003

[0139] [3]L.Zheng and D.N.C.Tse,「Diversity and multiplexing:a fundamental tradeoff in multiple-antenna channels」,IEEE Trans.Info.Th.,vol.49,no.5,pp.1073~1096,May 2003

[0140] [4]D.N.C.Tse,P.Viswanath,and L.Zheng,「Diversity-multiplexing tradeoff in multiple-access channels」,IEEE Trans.Info.Th.,vol.50,no.9,pp.1859~1874,Sept.2004

[0141] [5]E.Visotsky and U.Madhow,「Space-time transmit precoding with imperfect feedback」,IEEE Trans.Info.Th.,vol.47,pp.2632~2639,Sep.2001

[0142] [6]S.A.Jafar,S.Vishwanath,and A.Goldsmith,「Channel capacity and beamforming for multiple transmit and receive antennas with covariance feedback」,Proc.IEEE Int.Conf.on Comm.,vol.7,pp.2266~2270,Jun.2001

[0143] [7]S.A.Jafar and A.Goldsmith,「Transmitter optimization and optimality of beamforming for multiple antenna systems」,IEEE Trans.Wireless Comm.,vol.3,pp.1165~1175,July 2004

[0144] [8]E.A.Jorswieck and H.Boche,「Channel capacity and capacity-range of beamforming in MIMO wireless systems under correlated fading with covariance feedback」,IEEE Trans.Wireless Comm.,vol.3,pp.1543~1553,Sep.2004

[0145] [9]A.L.Moustakas and S.H.Simon,「Optimizing multiple-input single-output(MISO)communication systems with general Gaussian channels:nontrivial covariance and nonzero mean」,IEEE Trans.Info.Th.,vol.49,pp.2770~2780,Oct.2003。

[0146]

[10] M.Kang and M.S.Alouini,「Water-filling capacity and beamforming performance of MIMO systems with covariance feedback」,IEEE Work.on Sign.Proc.Adv.in Wire.Comm.,pp.556~560,June 2003。

[0147]

[11] S.H.Simon and A.L.Moustakas,「Optimizing MIMO antenna systems with channel covariance feedback」,IEEE Jour.Select.Areas in Comm.,vol.21,pp.406~417,Apr.2003。

[0148]

[12] S.M.Alamouti,「A simple transmit diversity technique for wireless communications」,IEEE Jour.Select.Areas in Comm.,vol.16,no.8,pp.1452~1458,Oct.1998。

[0149]

[13] V.Tarokh,N.Seshadri,and A.R.Calderbank,「Space-time codes for high data rate wireless communication:Performance criterion and code construction」,IEEE Trans.Info.Th.,vol.44,pp.744~65,Mar.1998。

[0150]

[14] V.Tarokh,H.Jafarkhani,and A.R.Calderbank,「Space-time block codes from orthogonal designs」,IEEE Trans.Info.Th.,vol.45,pp.1456~467,July 1999。

[0151]

[15] E.N.Onggosanusi,A.G.Dabak,and T.A.Schmidl,「High rate space-time block coded scheme:performance and improvement in correlated fading channels」,Proc.IEEE Wireless Comm.and Net.Conf.,vol.1,pp.194~199,Mar.2002。

[0152]

[16] G.D.Durgin,Space-Time Wireless Channels,Prentice Hall,Upper Saddle River,NJ,USA,2003

[0153]

[17] D.-S.Shiu,G.J.Foschini,M.J.Gans,and J.M.Kahn,「Fading correlation and its effect on the capacity of multielement antenna systems」,IEEE Trans.Comm.,vol.48,no.3,pp.502~513,Mar.2000。

[0154]

[18] A.Forenza and R.W.Heath Jr.,「Impact of antenna geometry on MIMP communication in indoor clustered channels」,Proc.IEEE Antennas and Prop.Symp.,vol.2,pp.1700~1703,June 2004。

[0155]

[19] E.A.Jorswieck and H.Boche,「Channel capacity and capacity-range of beamforming in MIMO wireless systems under correlated fading with covariance feedback,」IEEE Trans.Wireless Comm.,vol.3,pp.1543~1553,Sep.2004

[0156]

[20] R.W.Heath Jr.and A.Paulraj,「Switching between multiplexing and diversity based on constellation distance,」Proc.of Allerton Conf.on 208,Comm.Control and Comp.,Sep.2000。

[0157]

[21] S.Catreux,V.Erceg,D.Gesbert,and R.W.Heath Jr.,「Adaptive modulation and MIMO coding for broadband wireless data networks,」IEEE Comm.Mag.,vol.2,pp.108~115,June 2002。

[0158]

[22] A.Forenza,A.Pandharipande,H.Kim,and R.W.Heath Jr.,「Adaptive MIMO transmission scheme:Exploiting the spatial selectivity of wireless channels」,Proc.IEEE Veh.Technol.Conf.,vol.5,pp.3188~3192,May 2005。

[0159]

[23] C.B.Chae,A.Forenza,R.W.Heath,Jr.,M.R.McKay,and I.B.Collings,「Adaptive MIMO Transmission Techniques for Broadband Wireless Communication Systems」,IEEE Communications Magazine,vol.48,no.5,pp.112~118,May 2010

[0160]

[24] FCC,「Broadband action agenda」,National Broadband Plan,2010 http: / / www.broadband.gov / plan / national-broadband-plan-action-agenda.pdf

[0161]

[25] ,N.Delfas,F.Meunier,S.Flannery,T.Tsusaka,E.Gelblum and S.Kovler,「Mobile data wave:who dares to invest,wins」,Morgan Stanley Research Global,June 13,2012

[0162]

[26] D.Goldman,「Sorry,America:your wireless airwaves are full」,CNN Money http: / / money.cnn.com / 2012 / 02 / 21 / technology / spectrum_crunch / index.htm

[0163]

[27] P.Rysavy,「No silver bullets for FCC,NTIA spectrum challange」,Daily report for executives,Bloomberg BNA,Aug.2012 http: / / www.rysavy.com / Articles / 2012_09_No_Spectrum_Silver_Bullets.pdf

[0164]

[28] T.W.Hazlett,「Radio spectrum for a hungry wireless world」,Sept.22,2011

[0165]

[29] B.J.Love,D.J.Love and J.V.Krogmeier,「Like deck chairs on the Titanic:why spectrum reallocation won’t avert the coming data crunch but technology might keep the wireless industry afloat」,Feb.2012

[0166]

[30] Qualcomm,「The 1000x data challenge,the latest on wireless,voice,services and chipset evolution」,4G World,Oct.31st,2012

[0167]

[31] J.Lee,J.-K.Han,J.Zhang,「MIMO technologies in 3GPP LTE and LTE-advanced」,EURASIP Journal on Wireless Communications and Networking,Hindawi,May 2009

[0168]

[32] 3GPP,TS 36.201,「Evolved Universal Terrestrial Radio Access(E-UTRA);LTE Physical Layer-General Description(Release 8)」

[0169]

[33] 3GPP,TS 36.211,「Evolved Universal Terrestrial Radio Access(E-UTRA);Physical Channels and Modulation(Release 8)」

[0170]

[34] 3GPP,TS 36.212,「Evolved Universal Terrestrial Radio Access(E-UTRA);Multiplexing and channel coding(Release 8)」

[0171]

[35] 3GPP,TS 36.213,「Evolved Universal Terrestrial Radio Access(E-UTRA);Physical layer procedures(Release 8)」

[0172]

[36] T.Yoo,N.Jindal,and A.Goldsmith,「Multi-antenna broadcast channels with limited feedback and user selection」,IEEE Journal on Sel.Areas in Communications,vol.25,pp.1478~91,July 2007。

[0173]

[37] P.Ding,D.J.Love,and M.D.Zoltowski,「On the sum rate of channel subspace feedback for multi-antenna broadcast channels,」in Proc.,IEEE Globecom,vol.5,pp.2699~2703,November 2005。

[0174]

[38] N.Jindal,[MIMO broadcast channels with finite-rate feedback」,IEEE Trans.on Info.Theory,vol.52,pp.5045~60,November 2006。

[0175]

[39] D.J.Love,R.W.Heath,Jr.,V.K.N.Lau,D.Gesbert,B.D.Rao,and M.Andrews,「An Overview of Limited Feedback in Wireless Communication Systems」,IEEE Journal on Sel.Areas in Comm.,Special Issue on Exploiting Limited Feedback in Tomorrow’s Wireless Communication Networks,vol.26,no.8,pp.1341~1365,Oct.2008。

[0176] R.W.Heath,Jr.,D.J.Love,V.K.N.Lau,D.Gesbert,B.D.Rao,and M.Andrews,「Exploiting Limited Feedback in Tomorrow’s Wireless Communication Networks」,IEEE Journal on Sel.Areas In Comm.,Special Issue on Exploiting Limited Feedback in Tomorrow’s Wireless Communication Networks,vol.26,no.8,pp.1337~1340,Oct.2008。

[0177]

[41] D.J.Love,R.W.Heath,Jr.,and T.Strohmer,「Grassmannian Beamforming for Multiple-Input Multiple-Output Wireless Systems」,IEEE Trans.on Info.Theory special issue on MIMO Communication,vol.49,pp.2735~2747,Oct.2003。

[0178]

[42] C.B.Chae,D.Mazzarese,N.Jindal and R.W.Heath,Jr.,「Coordinated Beamforming with Limited Feedback in the MIMO Broadcast Channel」,IEEE Journal on Sel.Areas in Comm.,Special Issue on Exploiting Limited Feedback in Tomorrow’s Wireless Comm.Networks,vol.26,no.8,pp.1505~1515,Oct.2008。

[0179]

[43] A.Paulraj,「Is OFDMA,MIMO and OS the right stuff for mobile broad-band?」 http: / / www.ieeevtc.org / vtc2005fall / presentations / paulraj.pdf,Sept.2005

[0180]

[44] J.Wannstrom,「Carrier aggregation explained」,3GPP http: / / www.3gpp.org / Carrier-Aggregation-explained

[0181]

[45] 3GPP,TS 36.808,「Evolved Universal Terrestrial Radio Access(E-UTRA);Carrier Aggregation(Release 10)」,v10.0.0,June 2012

[0182]

[46] Nokia Siemens Networks,「2020:beyond 4G,radio evolution for the gigabit experience」,White Paper,2011,www.nokiasiemensnetworks.com

[0183]

[47] S.Marek,「AT&T’s Rinne talks about carrier aggregation trials,small cells and more」,http: / / www.fiercebroadbandwireless.com / story / atts-rinne-talks-about-carrier-aggregation-trials-small-cells-and-more / 2012-11-08

[0184]

[48] M.Reed,「InterfereX」,Tech23,2011 http: / / www.youtube.com / watch?v=YPpELm6iip8

[0185]

[49] NICTA,「InterfereX」, http: / / www.nicta.com.au / research / archive / research_themes / networked_systems / intererex

[0186]

[50] J.Duplicity,et al.,「MU-MIMO in LTE systems」,EURASIP Journal on Wireless Communications and Netowrking,Mar.2011

[0187]

[51] S.Feng and E.Seidel,「Self-organizing networks(SON)in 3GPP LTE」,Nomor research,May 2008

[0188]

[52] NEC,「Self organizing networks」,White paper,Feb.2009

[0189]

[53] U.S.Patent No.5,809,422,issued September 15,1998,entitled「Distributed microcellular communications system」,G.R.Raleigh,M.A.Pollack

[0190]

[54] G.J.Foschini,H.C.Huang,K.Karakayali,R.A.Valenzuela,and S,Venkatesan.The Value of Coherent Base Station Coordination.In Conference on Information Sciences and Systems(CISS 2005),Mar.2005。

[0191]

[55] M.K.Karakayali,G.J.Foschini,R.A.Valenzuela,and R.D.Yates,「On the maximum common rate achievable in a coordinated network」,Proc.of the Int’l Conf.on Communications(ICC’06),vol.9,pp.4333~4338,June 2006。

[0192]

[56] M.K.Karakayali,G.J.Foschini,and R.A.Valenzuela,「Network coordination for spectrally efficient communications in cellular systems」,IEEE Wireless Communications Magazine,vol.13,no.4,pp.56~61,Aug.2006。

[0193]

[57] G.J.Foschini,M.K.Karakayali,and R.A.Valenzuela,「Coordinating multiple antenna cellular networks to achieve enormous spectral efficiency」,Proceedings of the IEEE,vol.153,no.4,pp.548~555,Aug.2006。

[0194]

[58] S.Venkatesan,A.Lozano,and R.Valenzuela,「Network MIMO:overcoming inter-cell interference in indoor wireless systems」,Proc.of Asilomar conf.,pp.83~87,Nov.2007

[0195]

[59] S.Venkatesan,H.Huang,A.Lozano,and R.Valenzuela,「A WiMAX-based implementation of network MIMO for indoor wireless systems」,EURASIP Journal on Advances in Signal Processing,Sep.2009

[0196]

[60] Y.Liang,R.Valenzuela,G.Foschini,D.Chizhik,and A.Goldsmith,「Interference suppression in wireless cellular networks through picocells」,ACSSC,pp.1041~1045,Nov.2007

[0197]

[61] A.Papadogiannis,H.J.Bang,D.Gesbert,and E.Hardouin,「Efficient selective feedback design for multicell cooperative networks」,IEEE Trans.On Vehicular Techn.,pp.196~205,vol.60,n.1,Jan.2011

[0198]

[62] I.F.Akyildiz,D.M.Guterrez-Estevez,E.C.Reyes,「The evolution to 4G cellular systems:LTE-Advanced」,Physical Comm.,Elsevier,pp.217~244,2010。

[0199]

[63] A.Barbieri,P.Gaal,S.Geirhofer,T.Ji,D.Malladi,Y.Wei,and F.Xue,「Coordinated downlink multi-point communications in heterogeneous cellular networks」,(Qualcomm),Information Theory and App.Workshop,pp.7~16,Feb.2012

[0200]

[64] S.Parkvall,E.Dahlman,A.Furuskar,Y.Jading,M.Olsson,S.Wanstedt,and K.Zangi,「LTE-Advanced-evolving LTE towards IMT-Advanced」,(Ericsson)IEEE VTC,pp.1~5,Sep.2008

[0201]

[65] R.A.Monziano and T.W.Miller,Introduction to Adaptive Arrays,New York:Wiley,1980。

[0202]

[66] K.K.Wong,R.D.Murch,and K.B.Letaief,「A joint channel diagonalization for multiuser MIMO antenna systems」,IEEE Trans.Wireless Comm.,vol.2,pp.773~786,Jul 2003;

[0203]

[67] R.Chen,R.W.Heath,Jr.,and J.G.Andrews,「Transmit Selection Diversity for Unitary Precoded Multiuser Spatial Multiplexing Systems with Linear Receivers」,IEEE Trans.on Signal Proc.,vol.55,no.3,pp.1159~1171,Mar.2007。

[0204]

[68] M.Costa,「Writing on dirty paper」,IEEE Transactions on Information Theory,Vol.29,No.3,Page(s):439~441,May 1983。

[0205]

[69] G.Caire and S.Shamai,「On the achievable throughput of a multiantenna Gaussian broadcast channel」,IEEE Trans.Info.Th.,vol.49,pp.1691~1706,July 2003。

[0206]

[70] N.Jindal & A.Goldsmith,「Dirty Paper Coding vs.TDMA for MIMO Broadcast Channels」,IEEE Trans.on Info.Theory,vol.51,pp.1783~1794,May 2005。

[0207]

[71] M.Tomlinson,「New automatic equalizer employing modulo arithmetic」,Electronics Letters,Page(s):138~139,March 1971。

[0208]

[72] H.Miyakawa and H.Harashima,「A method of code conversion for digital communication channels with intersymbol interference,」Trans.of the Inst.of Electronic

[0209]

[73] U.Erez,S.Shamai(Shitz),and R.Zamir,「Capacity and lattice-strategies for cancelling known interference」,Proceedings of International Symposium on Information Theory,Honolulu,Hawaii,Nov.2000。

[0210]

[74] W.Yu and J.M.Cioffi,「Trellis Precoding for the Broadcast Channel」,IEEE Globecom,vol.2,pp.1344~1348,2001

[0211]

[75] B.M.Hochwald,C.B.Peel,and A.L.Swindlehurst,「A Vector-Perturbation Technique for Near-Capacity Multiantenna Multiuser Communication-Part I:Channel Inversion and Regularization」,IEEE Trans.On Communications,vol.53,n.1,pp.195~202,Jan.2005

[0212]

[76] B.M.Hochwald,C.B.Peel,and A.L.Swindlehurst,「A Vector-Perturbation Technique for Near-Capacity Multiantenna Multiuser Communication-Part II:Perturbation」,IEEE Trans.On Communications,vol.53,n.3,pp.537~544,Mar.2005

[0213]

[77] S.Perlman and A.Forenza,「Distributed-input distributed-output(DIDO)wireless technology:a new approach to multiuser wireless」,Rearden Labs White Paper,July 2011,http: / / www.reardenwireless.com / 110727-DIDO-A%20New%20Approach%20to%20Multiuser%20Wireless.pdf

[0214]

[78] A.Vance,「Steve Perlman’s wireless fix」,Businessweek,July 2011 http: / / www.businessweek.com / magazine / the-edison-of-silicon-valley-07272011.html

[0215]

[79] M.Lindstrom(Ericsson),「LTE-Advanced Radio Layer 2 and RRC aspects」,3GPP TSG-RAN WG2

[0216]

[80] Anritsu,「LTE resource guide」,www.us.anritsu.com

[0217]

[81] 3GPP,「Spatial Channel Model AHG(Combined ad-hoc from 3GPP & 3GPP2)」,SCM Text V6.0,April 22,2003

[0218]

[82] J.Lee,「Introduction of LTE-Advanced DL / UL MIMO」,Samsung Electronics,Sep.2009

[0219]

[83] E.Dahlman,S.Parkvall and J.Skold,「4G:LTE / LTE-Advanced for mobile broadband」,Elsevier,2011。

[0220]

[84] J.Syren,「Overview on the 3GPP long term evolution physical layer」,Freescale White Paper,July 2007

[0221]

[85] M.Baker,「LTE-Advanced physical layer」,Alcatel-Lucent,Dec.2009

[0222]

[86] J.Xu,「LTE-Advanced signal generation and measurements using SystemVue」,Agilent Technologies

[0223]

[87] X.Hou and H.Kayama,「Demodulation reference signal design and channel estimation for LTE-Advanced uplink」,DOCOMO,Adv.in Vehic.Netw.Tech.,Apr.2011

[0224]

[88] D.C.Chu,「Polyphase codes with good periodic correlation properties」,IEEE Trans.Info.Theory,vol.18,n.4,pp.531~532,July 1972。

[0225]

[89] A.Lozano,R.W.Heath and J.Andrews,「Fundamental limits of cooperation」,Mar.2012.http: / / arxiv.org / pdf / 1204.0011.pdf

[0226]

[90] J.G.Andrews,「Seven ways that HetNet are a cellular paradigm shift」 http: / / users.ece.utexas.edu / ~jandrews / pubs / And_HetNet_CommMag2012_v3.pdf

Claims

1. A multi-antenna system (MAS) with multi-user (MU) transmission ("MU-MAS") that increases the capacity of a wireless communication network by utilizing inter-cell multiplexing gain through spatial processing.

2. The system according to claim 1, characterized by comprising multiple distributed antennas interconnected to a centralized processor (CP) via a base station network (BSN) and using precoding to communicate with multiple client devices.

3. The system according to claim 2, characterized in that the wireless communication network is a cellular network such as an LTE network, the client device is an LTE user device (UE), the distributed antenna is an LTE-enhanced NodeB (eNodeB) or a mobility management entity (MME), the CP is an LTE gateway (GW), and the BSN is the interface of S1 or X1.

4. The system according to claim 3, characterized in that eNodeBs are grouped into "antenna clusters," each antenna cluster is associated with a different cell ID, and all eNodeBs from the same antenna cluster transmit the same cell ID via a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS).

5. The system according to claim 3, characterized in that all or a subset of DL resource blocks (RBs) are assigned to any UE, and simultaneous non-interfering data streams are transmitted from the BTS to the UE via precoding.

6. The system according to claim 5, characterized in that, in order to increase the data rate per user, precoding is used in combination with carrier aggregation (CA) and applied to different parts of the radio frequency (RF) spectrum (interband CA) or different bands within the same spectrum (intraband CA).

7. The system according to claim 2, characterized in that MU-MAS technology is gradually integrated into an existing LTE network.

8. The system according to claim 7, characterized in that the eNodeB and UE are compatible with LTE.

9. The system according to claim 7, characterized in that the eNodeB and UE utilize a modification of the LTE standard.

10. The system according to claim 7, characterized in that the LTE UE is updated to be compatible with MU-MAS.

11. The system according to claim 7, characterized in that a new generation of UE compatible with MU-MAS is deployed.

12. The system according to claim 7, characterized in that the LTE spectrum is subdivided to support a conventional cellular LTE eNodeB with one block of spectrum and a MU-MAS LTE eNodeB with another block of spectrum.

13. The system according to claim 7, characterized in that the conventional cellular LTE eNodeB is configured to cooperate with MU-MAS LTE eNodeB to share the same spectrum but operate in a time-division multiple access (TDMA) manner.

14. The system according to claim 7, characterized in that MU-MAS is used as a wireless backhaul for LOS or NLOS to an LTE small cell.

15. The system according to claim 7, characterized in that LTE small cells are gradually replaced with eNodeB.

16. The system according to claim 3, characterized in that the CP uses a round-robin, proportional fair, or greedy scheduler to schedule the UE for transmission on the DL or UL channel.

17. The system according to claim 16, characterized in that the scheduler uses CQI, sounding reference signal (SRS), spatial selectivity index (SSI), or a combination thereof as a performance measurement criterion for the scheduling method.

18. The system according to claim 17, characterized in that the scheduler selects an optimal subset of eNodeB and UE to be scheduled for transmission over a wireless link, based on SSI performance measurement criteria.

19. The system according to claim 16, characterized in that the scheduler selects a corresponding UE on the wireless link in order to minimize interference between antenna clusters or antenna subclusters.

20. The system according to claim 3, characterized in that a transmitting antenna selection method is applied across all eNodeBs to select the optimal eNodeB for current transmission on the DL channel.

21. The system according to claim 20, wherein the antenna selection method includes a queue of antenna subset IDs having corresponding priority numbers, and the antenna selection is applied to only a limited number of antenna subsets to reduce computational complexity.

22. The system according to claim 21, characterized in that the queue is subdivided into two or more groups using a round-robin rule and classification method in order to select a limited number of antenna subsets to be used by the antenna selection algorithm.

23. The system according to claim 6, characterized in that interband CA is enabled by operating one set of eNodeB at a lower carrier frequency and another set of eNodeB at a higher carrier frequency, so that the two sets intersect or one set is a subset of the other set.

24. The system according to claim 6, wherein the MU-MAS having precoding uses a CA method in combination with a frequency hopping pattern to improve robustness against frequency-selective fading or interference.

25. The system according to claim 3, characterized in that the MU-MAS uses a linear precoding method (e.g., zero-forcing, block diagonalization, matrix inversion, etc.).

26. The system according to claim 3, characterized in that the MU-MAS uses a nonlinear precoding method (for example, dirty paper coding or Tomlison-Harashima precoding, grid technique or trellis precoding, or vector perturbation technique).

27. The system according to claim 3, characterized in that the MU-MAS dynamically switches between linear and nonlinear precoding methods based on the number of UEs and eNobeBs in the antenna cluster and user cluster to reduce the computational complexity in the CP.

28. The system according to claim 3, characterized in that the MU-MAS switches between a precoding multiplexing method for UEs experiencing good channel quality (e.g., near eNodeB) and a beamforming or diversity method for UEs experiencing poor link quality (e.g., far from eNodeB).

29. The system according to claim 4, characterized in that only one eNodeB among all eNodeBs within the same antenna cluster or antenna subcluster transmits the LTE broadcast channels (e.g., P-SS and S-SS) to all UEs.

30. The system according to claim 29, characterized in that the eNodeB that transmits the LTE broadcast channel is selected to maximize the power received by the UE on the broadcast channel.

31. The system according to claim 29, wherein only a limited set of BTSs is selected to simultaneously transmit the LTE broadcast channel to all UEs, so that destructive interference is avoided at the UEs.

32. The system according to claim 4, characterized in that the LTE broadcast channel is transmitted with a power higher than the payload so as to reach all UEs within the same antenna cluster or antenna subcluster.

33. A method implemented within a multi-antenna system (MAS) with multi-user (MU) transmission ("MU-MAS") that increases the capacity of a wireless communication network by utilizing inter-cell multiplexing gain through spatial processing.

34. The method according to claim 33, characterized by comprising multiple distributed antennas interconnected to a centralized processor (CP) via a base station network (BSN) and using precoding to communicate with multiple client devices.

35. The method according to claim 34, characterized in that the wireless communication network is a cellular network such as an LTE network, the client device is an LTE user device (UE), the distributed antenna is an LTE-enhanced NodeB (eNodeB) or a mobility management entity (MME), the CP is an LTE gateway (GW), and the BSN is the interface of S1 or X1.

36. The method according to claim 35, characterized in that eNodeBs are grouped into "antenna clusters," different cell IDs are associated with each antenna cluster, and all eNodeBs from the same antenna cluster transmit the same cell ID via a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS).

37. The method according to claim 35, characterized in that all or a subset of DL resource blocks (RBs) are assigned to any UE, and simultaneous non-interfering data streams are transmitted from the BTS to the UE via precoding.

38. The method according to claim 37, characterized in that, in order to increase the data rate per user, precoding is used in combination with carrier aggregation (CA) and applied to different parts of the radio frequency (RF) spectrum (interband CA) or different bands within the same spectrum (intraband CA).

39. The method according to claim 34, characterized in that MU-MAS technology is gradually integrated into an existing LTE network.

40. The method according to claim 39, wherein the eNodeB and UE are compatible with LTE.

41. The method according to claim 39, characterized in that the eNodeB and UE utilize a modification of the LTE standard.

42. The method according to claim 39, wherein the LTE UE is updated to be compatible with MU-MAS.

43. The method according to claim 39, characterized in that a new generation of UE compatible with MU-MAS is deployed.

44. The method according to claim 39, characterized in that the LTE spectrum is subdivided to support a conventional cellular LTE eNodeB with one block of spectrum and a MU-MAS LTE eNodeB with another block of spectrum.

45. The method according to claim 39, characterized in that the conventional cellular LTE eNodeB is configured to operate in a time-division multiple access (TDMA) scheme, sharing the same spectrum in cooperation with MU-MAS LTE eNodeB.

46. The method according to claim 39, characterized in that MU-MAS is used as a wireless backhaul for LOS or NLOS to an LTE small cell.

47. The method according to claim 39, characterized in that the LTE small cells are gradually replaced with eNodeB.

48. The method according to claim 35, characterized in that the CP uses a round-robin, proportional fair, or greedy scheduler to schedule the UE for transmission on the DL or UL channel.

49. The method according to claim 48, characterized in that the scheduler uses CQI, sounding reference signal (SRS), spatial selectivity index (SSI), or a combination thereof as a performance measurement criterion for the scheduling method.

50. The method according to claim 49, characterized in that the scheduler selects an optimal subset of eNodeB and UE to be scheduled for transmission over a wireless link, based on SSI performance measurement criteria.

51. The method according to claim 48, characterized in that the scheduler selects a corresponding UE on the wireless link in order to minimize interference between antenna clusters or antenna subclusters.

52. The method according to claim 35, characterized by applying a transmitting antenna selection method across all eNodeBs to select the optimal eNodeB for current transmission on the DL channel.

53. The method according to claim 52, wherein the antenna selection method includes a queue of antenna subset IDs having corresponding priority numbers, and the antenna selection is applied to only a limited number of antenna subsets to reduce computational complexity.

54. The method according to claim 53, characterized in that the queue is subdivided into two or more groups using a round-robin rule and classification method in order to select a limited number of antenna subsets to be used by the antenna selection algorithm.

55. The method according to claim 38, characterized in that interband CA is enabled by operating one set of eNodeB at a lower carrier frequency and another set of eNodeB at a higher carrier frequency, so that the two sets intersect or one set is a subset of the other set.

56. The method according to claim 38, characterized in that the MU-MAS having precoding uses a CA method in combination with a frequency hopping pattern to improve robustness against frequency-selective fading or interference.

57. The method according to claim 35, characterized in that the MU-MAS uses a linear precoding method (e.g., zero-forcing, block diagonalization, matrix inversion, etc.).

58. The method according to claim 35, characterized in that the MU-MAS uses a nonlinear precoding method (for example, dirty paper coding or Tomlison-Harashima precoding, grid technique or trellis precoding, vector perturbation technique).

59. The system according to claim 35, characterized in that the MU-MAS dynamically switches between linear and nonlinear precoding methods based on the number of UEs and eNobeBs in the antenna cluster and user cluster to reduce the computational complexity in the CP.

60. The method according to claim 35, characterized in that the MU-MAS switches between a precoding multiplexing method for UEs experiencing good channel quality (e.g., near eNodeB) and a beamforming or diversity method for UEs experiencing poor link quality (e.g., far from eNodeB).

61. The method according to claim 36, characterized in that only one eNodeB among all eNodeBs in the same antenna cluster or antenna subcluster transmits the LTE broadcast channels (e.g., P-SS and S-SS) to all UEs.

62. The method according to claim 61, characterized in that the eNodeB that transmits the LTE broadcast channel is selected to maximize the power received by the UE on the broadcast channel.

63. The method according to claim 61, wherein only a limited set of BTSs is selected to simultaneously transmit the LTE broadcast channel to all UEs, such that destructive interference is avoided at the UEs.

64. The method according to claim 36, characterized in that the LTE broadcast channel is transmitted with a power higher than the payload so as to reach all UEs within the same antenna cluster or antenna subcluster.

Images