Systems for radio frequency calibration exploiting channel reciprocity in distributed input distributed output wireless communications

Abstract

This invention describes a system and method for applying uplink / downlink channel reciprocity to radio frequency (RF) calibration in a multi-antenna system (MAS) with multiple user (MU) transmissions ("MU-MAS"). This RF calibration is used to calculate an open-loop downlink precoder based on uplink channel estimation, thereby avoiding the feedback of channel state information as in a closed-loop scheme. For example, one embodiment of the MU-MAS includes a wireless cellular network having one or more beacon stations, multiple user terminal devices, and multiple distributed antennas that operate cooperatively via precoding methods to eliminate inter-user interference and increase network capacity.

Description

Technical Field

[0001] This invention relates to systems and methods for applying channel interchange for radio frequency calibration, and more specifically, to systems and methods for applying channel interchange for radio frequency calibration in a multi-user multi-antenna system (MU-MAS). Prior Technology

[0002] Over the past three decades, the wireless cellular market has witnessed a continuous increase in the number of users worldwide and a growing demand for better services, from voice shifting 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 a radical evolution of wireless technologies through various standards. This evolution began 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 UMTS and CDMA2000 (for web browsing) in the early 2000s, and finally, LTE (for high-speed internet connectivity) currently being deployed in various countries around the world.

[0003] Long Term Evolution (LTE) is a standard developed by the 3rd Generation Partnership Project (3GPP) for fourth-generation (4G) cellular systems. LTE theoretically achieves up to 4x improvement in downlink spectral efficiency compared to previous 3G and HSPA+ standards by utilizing spatial components of the radio channel through Multiple-Input Multiple-Output (MIMO) technology. Advanced LTE is theoretically an evolution of the currently standardized LTE that will achieve up to 8x improvement in spectral efficiency compared to the 3G standard system.

[0004] Despite this technological evolution, wireless carriers are highly likely to be unable to meet the growing demand for data rates over the next three years due to increased market penetration of data-hungry applications such as live HD video streaming, video conferencing, and gaming on smartphones and tablets. Wireless network capacity is estimated to grow by 5x in Europe from 2011 to 2015 due to improved technologies (such as LTE) and increased spectrum availability from governments

[25] . For example, as part of the national broadband plan

[24] , the FCC plans to open 500 MHz of spectrum by 2020 (300 MHz of which will be available by 2015) to promote wireless internet connectivity across the US. Unfortunately, capacity usage forecasts for 2015 are 23x higher in Europe than in 2011

[25] and a similar spectrum shortage is expected in the US by 2014 [26-27]. As a result of this data processing, revenue from wireless carriers may fall below their CAPEX and OPEX, thus having a potentially devastating impact on the wireless market

[28] .

[0005] Since the capacity gain and increased spectrum availability provided by LTE deployment are insufficient, the only foreseeable solution to prevent this impending spectrum crisis is to promote new wireless technologies.

[29] Advanced LTE (an evolution of the LTE standard) promises to offer additional gains over LTE through more sophisticated MIMO technology and by increasing the density of “small cells.”

[30] However, there are limitations on the number of cells that can be suited to a specific area without causing interference problems or increasing the complexity of backhaul transmission to allow for coordination across cells.

[0006] A promising technology that will provide orders-of-magnitude increases in spectral efficiency over conventional cellular systems without limiting conventional cellular systems is Distributed Input Distributed Output (DIDO) technology (see the related patents and applications mentioned above in [0002-0020]). This invention describes DIDO technology employed in the context of cellular systems (such as LTE or Advanced LTE) that are both constrained and unconstrained by cellular standards to provide significant performance benefits over conventional wireless systems. It begins with an overview of MIMO and reviews the different spatial processing techniques employed in LTE and Advanced LTE. Then, it demonstrates how this invention provides significant capacity gains for next-generation wireless communication systems compared to prior art methods.

[0007] MIMO employs multiple antennas at both the transmitter and receiver sides of the wireless link and uses spatial processing to improve link reliability through diversity techniques (i.e., diversity gain) or to provide higher data rates through multiplexing schemes (i.e., multiplexing gain) [1-2]. Diversity gain is a measure of enhanced robustness to signal fading, resulting in a higher signal-to-noise ratio (SNR) at a fixed data rate. Multiplexing gain is achieved by utilizing the additional spatial degrees of freedom of the wireless channel to increase the data rate with a fixed error probability. The basic trade-off between diversity and multiplexing in MIMO systems is explained in [3-4].

[0008] In practical MIMO systems, link adaptation techniques can be used to dynamically switch between diversity and multiplexing schemes based on propagation conditions [20-23]. For example, the link adaptation schemes described in [22-23] demonstrate that beamforming or orthogonal space-time block codes (OSTBCs) are superior in channels with low SNR or characterized by low spatial selectivity. In contrast, spatial multiplexing can provide significant gains in data rates for channels with high SNR and high spatial selectivity. For example, [picture] [1] The cell can be divided into two zones: i) a multiplexing zone 101, characterized by high SNR (due to proximity to cell towers or base stations), where spatial multiplexing can be used to apply the spatial degrees of freedom of channels to increase data rate; ii) a diversity zone 102 or cell edge, where spatial multiplexing is less effective and diversity methods can be used to improve SNR and coverage (resulting only in a marginal increase in data rate). Note that [picture] [1] In the large community 103 circle, the shaded center of the circle is marked as "multi-functional area" and the non-shaded outer area of ​​the circle is marked as "diversity area". (The last part is incomplete and likely refers to a specific area or process.) [picture] [1] [,picture] [3] [To the image] [5] Use this same area designation, where shaded areas are "multitasking areas" and unshaded areas are "diversity areas," even if they are not explicitly labeled. For example, the same designation is used for... [picture] [1] 104 small residential communities.

[0009] The LTE (Version 8) and Advanced LTE (Version 10) standards define a set of ten transmission modes (TM) including one of the diversity or multiplexing schemes [35, 85-86]: Mode 1: Single antenna port, port 0 Mode 2: Transport Diversity Mode 3: Large Delay Cyclic Delay Diversity (CDD), an extension of open-loop spatial multiplexing in single-user MIMO (SU-MIMO). Mode 4: SU-MIMO Closed-Loop Spatial Multiplexing Mode 5: Multi-user MIMO (MU-MIMO) Mode 6: Closed-loop spatial multiplexing using a single transport layer Mode 7: Single antenna port, UE-specific RS (port 5) Mode 8: Single-layer or double-layer transmission for UE-specific RS (port 7 and / or port 8) Mode 9: Single-layer or up to eight-layer closed-loop SU-MIMO (added in version 10) Mode 10: Multi-layer closed-loop SU-MIMO, up to eight layers (added in version 10) The following sections describe common diversity and multiplexing schemes used in cellular systems, as well as specific methods employed in LTE as outlined above, and compare them with technologies unique to DIDO communication. First, two types of transmission methods are identified: i) intra-cell methods (applying micro-diversity in cellular systems), which use multiple antennas to improve link reliability or data rate within a single cell; ii) inter-cell methods (applying macro-diversity), which allow cooperation between cells to provide additional diversity or multiplexing gain. Then, it is explained how the present invention provides significant advantages over prior art (including spectral capacity gain). [1.] [Internal Diversity Method] [ ]

[0010] Intracellular diversity methods operate within a single cell and are designed to increase SNR in scenarios with poor link quality (e.g., users at the cell edge experience high path loss from the central tower or base station). Typical diversity schemes used in MIMO communication are beamforming [5-11] and orthogonal space-time block code (OSTBC) [12-15].

[0011] The diversity techniques supported by the LTE standard are transport diversity, closed-loop rank-1 precoding, and dedicated beamforming [31-35]. The transport diversity scheme supports two or four transmit antennas on the downlink (DL) and only two antennas on the uplink (UL). In the DL channel, it is implemented via a space-frequency block code (SFBC) combined with frequency-switched transport diversity (FSTD) to apply spatial and frequency selectivity

[31] . Rank-1 precoding forms a dedicated beam for one user based on quantized weights selected from a codebook (pre-designed using finite feedback techniques [36-42]) to reduce the beam size from the user equipment (UE) to the base transceiver station (BRT). [picture] [1] The feedback addition of BTS 105 (or eNodeB in LTE terminology). Alternatively, dedicated beamforming weights can be calculated based on UE-specific reference signals. [2.] [Multi-tasking methods within the community] [ ]

[0012] MIMO multiplexing schemes [1, 19] provide data rate gains to support multiple parallel data streams on a wireless link in high SNR scenarios and in scenarios with sufficient spatial degrees of freedom in the channel (e.g., multipath-rich environments with high spatial selectivity [16-18]).

[0013] The LTE standard supports different 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 uses feedback information from the UE to select DL precoding weights; ii) open loop, which is used when feedback from the UE is unavailable or the UE moves too fast to support the closed loop scheme. The closed loop scheme uses a set of pre-computed weights selected from a codebook. These weights can support two or four transmit antennas and one to four parallel data streams (identified by several layers of the precoding matrix) depending on the UE request and the scheduler decision at the BTS. Advanced LTE will include a new transmission mode of up to MIMO 8 × 8 to provide up to 8x increase in spectral efficiency through spatial processing

[62] .

[0014] The MU-MIMO scheme is defined for both UL channels and DL channels [31, 50]. In UL, each UE sends a reference signal to the BTS (consisting of a cyclically shifted version of the Zadoff-Chu sequence

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

[0015] Intra-cell multiplexing techniques employing spatial processing only provide satisfactory performance in propagation scenarios characterized by high SNR (or SINR) and high spatial selectivity (multipath-rich environments). For conventional large cells, these conditions may be difficult to achieve because the BTS is usually far from the UE and the SINR distribution is usually centered on low values ​​

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

[0016] Other technologies and network solutions covered by Advanced LTE that achieve additional multiplexing gains (without requiring spatial processing via MIMO) include carrier aggregation (CA) and small cells. CA [30, 44-47] combines different portions of the RF spectrum to increase the signal bandwidth by up to 100 MHz

[85] , thereby generating higher data rates. Intra-band CA combines different frequency bands within the same portion of the spectrum. Therefore, it can use the same RF chain for multiple channels and recombine multiple data streams in software. Inter-band CA requires different RF chains to operate at different portions of the spectrum and requires signal processing to recombine multiple data streams from different frequency bands.

[0017] The key idea behind small cells [30, 47] is to reduce the size of conventional large cells, thereby allowing for higher cell density and greater transmission capacity per coverage area. Small cells typically utilize low-power transmission (such as...) [picture] [1] The cheap access point 106 is deployed instead of the tall and expensive cell towers used for large cells. Advanced LTE defines two types of small cells: i) metro cells, which are used for outdoor installations in urban areas and support up to 32 to 64 simultaneous users; and ii) micro cells, which are used indoors and can serve up to 4 active users. One advantage of small cells is that the density of UEs close to the BTS is statistically higher, resulting in better SNR that can be applied through spatial multiplexing to increase data rates. However, there are still many concerns about the practical deployment of small cells (specifically, related to backhaul transmission). In fact, reaching each small cell to the BTS via high-speed wired connections can be challenging, especially considering the high density of metro cells and micro cells in a given coverage area. While line-of-sight (LOS) backhaul to small cells is generally cheaper to implement than wired backhaul, there is typically no practical LOS backhaul path available for optimal small cell BTS placement, nor is there a general solution for non-line-of-sight (NLOS) wireless backhaul to small cell BTSs. Furthermore, small cells require complex real-time coordination across BTSs to avoid interference as seen in ad hoc networks (SON) [30, 51-52] and sophisticated cell planning tools (even more complex than conventional cellular systems due to the higher density of small cells) to plan their optimal locations [48, 49]. Finally, handover is a limiting factor in small cell deployments, particularly in scenarios where simultaneous cell switching by groups of users results in numerous handover add-ons on the backhaul, leading to high latency and unavoidable call drops.

[0018] A practical, general solution can be simply demonstrated where it is impossible to achieve optimal or necessary uniformly improved throughput by allowing small cells to coexist with large cells. Among countless such unsolvable situations is the inevitable overlap of UE transmissions in a small cell with those in a large cell, where both use the same frequency to reach their respective UEs. Clearly, in this case, the large cell transmission will interfere with the small cell transmission. While there may be methods to mitigate this interference for specific situations involving a particular large cell, a particular small cell, the large cell and the involved small cell UEs, their throughput requirements, and environmental conditions, any such method will be highly specific not only to the static planning of the large and small cells but also to the dynamic situation over a specific time interval. Typically, achieving full throughput from the channel to each UE is not possible. [3.] [Interval Partitioning Method] [ ]

[0019] In heterogeneous networks (HetNets) where large and small cells (e.g., metro cells, micro cells, and micro cells) coexist

[90] , different techniques are required to eliminate inter-cell interference. While HetNets offer better coverage through small cells, the data rate gain is marginal because they require sharing the spectrum through different forms of frequency reuse or spatial processing to remove interference rather than achieving multiplexing gain. The LTE standard employs an inter-cell interference coordination (ICIC) scheme to remove (specifically) interference at cell edges. There are two types of ICIC methods: cell autonomy and coordination between BTSs.

[0020] Community self-regulation ICIC scheme approved [picture] [2] illustrates different frequency reuse patterns to avoid inter-cell interference, where hexagons represent cells and colors indicate different carrier frequencies. LTE considers three types of schemes: i) full frequency reuse (or reuse 1), where the cell utilizes all available bandwidth (e.g., in...). [picture] [2a]), thereby generating high interference at the cell edge; ii) Hard Frequency Reuse (HFR), in which each cell is assigned a different frequency band (e.g., in [picture] [2b] (with a typical reuse factor of 3) to avoid interference across adjacent cells; iii) Partial Frequency Reuse (FFR), where the center of the cell is assigned the entire available bandwidth as in Frequency Reuse 1, while the cell edges operate in HFR mode to mitigate inter-cell interference, as in [picture] [2c] in.

[0021] The coordinated ICIC method enables cross-BTS cooperation to improve the performance of wireless networks. This technique is a special case of the method taught in related patents and applications [0002-0022] to achieve cross-transceiver cooperation in the general case of a distributed antenna network in which multiple UEs use the same frequency simultaneously.

[53] describes cross-BTS cooperation to remove inter-cell interference for a cellular system of a single UE at a given frequency at a given time. The system in

[53] divides each large cell into multiple sub-cells and achieves soft handover across sub-cells by using dedicated beamforming from a coordinated BTS to improve the link robustness of a single UE at a single frequency as it moves along the sub-cell boundaries.

[0022] Recently, in MIMO literature, such cooperative wireless cellular networks are defined as "network MIMO" or "Coordinated Multipoint" (CoMP) systems. [54-61] presents theoretical analysis and simulation results regarding the benefits gained in network MIMO by eliminating inter-cell interference. The key advantage of network MIMO and CoMP is the removal of the interference required for large cells. [picture] [3] Inter-cell interference in the overlapping area of ​​the cell 301, which is referred to as "interference area".

[0023] CoMP networks have proactively become part of the advanced LTE standard as a solution to mitigate inter-cell interference in next-generation cellular networks [62-64]. To date, three CoMP solutions have been proposed in standards for removing inter-cell interference: i) Coordinated Scheduling / Beamforming (CS / CB), where the UE receives its data stream from only one BTS via beamforming and achieves cross-BTS coordination to remove interference via beamforming or scheduling techniques; ii) Dynamic Cell Selection (DCS), which transparently and dynamically selects the cell for each UE on a per-subframe basis; and iii) Joint Transmission (JT), where data for a given UE is jointly transmitted from multiple BTSs to improve received signal quality and eliminate inter-cell interference. CoMP-JT achieves greater cross-BTS coordination at the cost of higher overhead in reload transmission compared to CoMP-CS / CB. [4.] [Inter-area multiplexing method] [ ]

[0024] Prior art multi-user wireless systems add complexity and introduce limitations to wireless networks, resulting in a situation where the experience of a given user (e.g., available bandwidth, latency, predictability, reliability) is affected by the spectrum utilization by other users in the area. Given the increasing demand for aggregated bandwidth within a shared wireless spectrum and the growing need for applications from a given user to rely on the reliability, predictability, and low latency of a multi-user wireless network, it is evident that prior art multi-user wireless technologies have numerous limitations. In fact, given the limited availability of spectrum suitable for certain types of wireless communication (e.g., wavelengths that efficiently penetrate building walls), prior art wireless technologies are insufficient to meet the increasing demand for reliable, predictable, and low-latency bandwidth.

[0025] Previous intracellular diversity and multiplexing techniques could theoretically increase the throughput of current cellular networks by up to 4x for LTE (via MIMO 4 × 4) or up to 8x for advanced LTE (via MIMO 8 × 8), but higher-order MIMO achieves an improvement in the reduction of increasing throughput in a given multipath environment, especially when UEs (such as smartphones) become smaller and more constrained in terms of antenna placement. Additional marginal throughput gains in next-generation cellular systems can be obtained from additional spectrum allocations applied via carrier aggregation techniques (e.g., FCC National Broadband Program) and from denser distribution of BTSs via small cell networks and SON [30, 46]. However, all of the above techniques still heavily rely on spectrum or time-sharing techniques to achieve multi-user transmission, as the spectral efficiency gains obtained through spatial processing are limited.

[0026] While previous inter-cell approaches (e.g., network MIMO and CoMP systems [53-64]) could improve the reliability of cellular networks by eliminating inter-cell interference, their capacity gains were only marginal. In practice, these systems constrained the power transmitted from each BTS to be contained within the cell boundary and effectively eliminated only inter-cell interference caused by power leakage across cells. [picture] [3] An example of a cellular network with three BTSs is shown, each BTS being characterized by its own coverage area or cell. Power transmitted from each BTS is constrained to limit interference across cells, as in... [picture] [3] illustrates the area of ​​cell overlap. When such systems operate in low SINR mode in the interference zone, the gain in their spectral efficiency is marginal, similar to that of intra-cell schemes for SU-MIMO. To truly achieve significant capacity gains in inter-cell cooperative networks, the power constraints at cell boundaries must be relaxed and spatial multiplexing should be achieved through cells with high SINR (not only at the edges of cells with poor SINR performance, as in previous techniques).

[0027] [picture] [4] This demonstrates a scenario where the increased power from the simultaneous transmission of the three BTSs 401 at the same frequency allows for interference at a higher level across one of the cells 402. In prior art systems, this interference would result in incoherent interference (interruption of UE signal reception) across the interference area of ​​the BTS. However, this interference is actually applied in this invention using a novel inter-cell multiplexing method with spatial processing to create a coherent interference area around each UE (enhancing UE signal reception), thereby providing simultaneous non-interfering data streams to each UE and increasing its SINR across the cell.

[0028]

[89] describes specific cases of honeycomb systems. [picture] The scenario illustrated in [4]. The system in

[89] consists of several BTSs that identify different cells forming a cluster. Cooperation across BTSs is only allowed from adjacent cells within the same cluster. In this scenario, it is shown that there is a limitation on the capacity (or spectral efficiency) that can be achieved through inter-cell multiplexing when the power transmitted from the BTS increases. In fact, as the transmission power increases, the interference outside the cluster increases proportionally, resulting in SINR and thus a saturation pattern of capacity. As a result of this effect, the system in

[89] can theoretically achieve a maximum capacity gain of 3x (i.e., a maximum of three cells within the cluster), and any additional cells included in the cluster will have reduced capacity due to increased interference outside the cluster (e.g., the case of 21 cells per cluster produces a lower capacity than the case of 3 cells per cluster). It is observed that the basic capacity limitation in

[89] is maintained by the BTS being constrained to a predefined position (as in a cellular system), and the multiplexing gain is achieved by increasing the transmission power from the BTS. To obtain theoretically unlimited capacity gain through inter-cell multiplexing, the constraints on BTS placement must be removed, thus allowing BTS to be placed anywhere convenient.

[0029] Therefore, it is expected to provide a system that achieves an order-of-magnitude increase in spectral efficiency by removing the power of the distributed BTS 501 transmission and any constraints on its placement through spatial processing. [picture] [5] Demonstrates one example in which numerous additional access points 502 are added to intentionally increase the level of incoherent interference across cell 503, which is applied in this invention to generate coherent interference around the UE, thereby generating theoretically unrestricted inter-cell multiplexing gain. The additional access points are casually placed anywhere convenient and are not restricted to any particular cell plan, such as in cellular systems described in the prior art. In one exemplary embodiment of the invention, the casual access points are distributed input distributed output (DIDO) access points and the inter-cell multiplexing gain is achieved through the DIDO methods described in [0014-0020] and [77-78]. In another embodiment, the casual access points are similar to low-cost Wi-Fi access points or low-power transceivers in small cells [30, 47], thereby providing a smaller coverage area that overlaps across a large cell, such as... [picture] As shown in [5].

[0030] It has been observed that previous inter-cell methods [53-64] achieved this by intentionally limiting the transmission power from each BTS (e.g., in...). [picture] [3] In order to avoid incoherent interference and eliminate residual inter-cell interference (in overlapping areas between cells) through spatial processing, thereby providing improved SINR and inter-cell diversity gain. It is further observed that

[89] BTS placement is constrained to the cell plan when increasing transmission power, thereby limiting the achievable capacity due to out-of-cluster interference and thus it is still interference-limited. In contrast, the present invention uses incoherent interference to form coherent interference around the UE by transmitting higher power from each BTS placed by chance, thereby improving the signal quality at the UE, which is a necessary condition, to obtain inter-cell multiplexing gain through the cell through spatial processing. Therefore, the system described in the prior art cannot be used to achieve unrestricted inter-cell multiplexing gain through spatial processing because there is no sufficient SINR through the cell (due to limited transmission power from BTS or out-of-cluster interference when increasing transmission power) as in the inter-cell multiplexing method of the present invention. In addition, the system described in the prior art will not be able to operate to achieve [picture] [4] [To the image] The multiplexing gain achieved in this invention, as illustrated in [5], assumes that prior art systems were designed to avoid [picture] [1] [and illustrations] [3] [To the image] [5] shows inter-cell interference within the diversity region, rather than applying inter-cell interference in the multitasking region to achieve the inter-cell multiplexing gain as achieved in this invention. Summary of the Invention

[0031] The present invention relates to a multi-antenna system (MAS) (“MU-MAS”) with multiple user (MU) transmission that employs radio frequency (RF) calibration and applies reciprocity between downlink (DL) and uplink (UL) channels. The MU-MAS consists of multiple distributed antennas, multiple user terminal devices, and one or more beacon stations. Simple Explanation of the Diagram

[0032] A better understanding of the invention will be obtained from the following detailed description, together with the accompanying drawings, in which: [picture] [1] The diagram illustrates the multi-work zone and distribution zone used in a large community and a small community. [picture] [2a] Illustrated illustration of a full-frequency reusable pattern in a conventional honeycomb system. [picture] [2b]Illustrated illustration of a hard frequency reuse (HFR) pattern in a conventional honeycomb system. [picture] [2c]Illustration of a partial frequency reuse (FFR) pattern in a conventional honeycomb system. [picture] [3] Illustrated explanation of the interference zone between adjacent large residential areas. [picture] [4] A diagram illustrating multiple BTSs that transmit at higher power to increase interference between cells. [picture] [5] The diagram illustrates one example of adding numerous access points to deliberately increase the accuracy of incoherent interference throughout the cell. [picture] [6] Illustrated explanation of network components in an LTE network. [picture] [7a] Illustrated diagram of the LTE frame structure used for FDD operation. [picture] [7b] Illustrated diagram of the LTE frame structure used for TDD operation. [picture] [8a] Illustrated explanation of LTE "resource elements" and "resource blocks" in an OFDM DL channel. [picture] [8b] Illustrated explanation of LTE "resource elements" and "resource blocks" in an SC-FDMA UL channel. [picture] [9] An embodiment of a multi-user (MU) multi-antenna system (MAS) or MU-MAS consisting of an antenna cluster and a user cluster is illustrated. [picture]

[10] Illustrated an embodiment of a MU-MAS, in which a different cell ID is associated with each antenna subcluster. [picture]

[11] Illustrated an embodiment of a MU-MAS, wherein the same set of cell IDs is assigned to antenna subclusters with a given repeating pattern. [picture]

[12] A diagram illustrating the SNR distribution of a practical deployment of the MU-MAS system in downtown San Francisco, California, including sparsely populated and densely populated areas. [ ] [picture]

[13] Illustrated an embodiment of a MU-MAS consisting of a CP, a distributed BTS and multiple UEs. [ ] [picture]

[14] The diagram illustrates an embodiment of a MU-MAS consisting of a CP, a distributed BTS, multiple devices, and a UE connected to the devices and BTS via a network interface. [ ] [picture]

[15] Illustrated an embodiment of a MU-MAS, wherein the UE is in a housing that is physically attached to a user device. [ ] [picture]

[16] Illustrated an embodiment of a MU-MAS in which distributed antennas communicate to the UE via UL and DL channels. [ ] [picture]

[17] Illustrated an embodiment of a MU-MAS in which distributed antennas communicate to a beacon station via UL and DL channels. [ ] [picture]

[18] The diagram illustrates the symbol error rate (SER) performance of MU-MAS with linear precoding in the presence / absence of RF mismatch and in the presence / absence of RF calibration. [ ] [picture]

[19] The figure illustrates the symbol error rate (SER) performance of MU-MAS with and without RF mismatch and with and without RF calibration, using linear and nonlinear precoding. [ ] [picture] [20a] [,picture] [20b] Illustrated diagram of the 4-QAM constellation at the UE (before the modulus operation) when applying THP nonlinear precoding. Implementation

[0033] [ ] [Related Applications] [ ] This application may relate to the following concurrently filed U.S. patent applications: U.S. Application No. 13 / 797,984, entitled "Systems and Methods for exploiting inter-cell multiplexing gain in wireless systems via distributed input distributed output technology" U.S. Application No. 13 / 797,971, entitled "Systems and Methods for exploiting inter-cell multiplexing gain in wireless systems via distributed input distributed output technology" U.S. Application No. 13 / 797,950, entitled "Systems and Methods for exploiting inter-cell multiplexing gain in wireless systems via distributed input distributed output technology" U.S. Application No. 13 / 633,702, entitled "Systems and Methods for wireless backhaul in distributed-input distributed-output wireless systems" U.S. Application No. 13 / 475,598, entitled "Systems and Methods to enhance spatial diversity in distributed-input distributed-output wireless systems" U.S. Application No. 13 / 233,006, entitled "System and Methods for planned evolution and obsolescence of multiuser spectrum" U.S. Application No. 13 / 232,996, entitled "Systems and Methods to Exploit Areas of Coherence in Wireless Systems" U.S. Application No. 13 / 464,648, entitled "System and Methods to Compensate for Doppler Effects in Distributed-Input Distributed Output Systems" U.S. Application No. 12 / 917,257, entitled "Systems and Methods To Coordinate Transmissions In Distributed Wireless Systems Via User Clustering" U.S. Application No. 12 / 802,988, entitled "Interference Management, Handoff, Power Control and Link Adaptation in Distributed-Input Distributed-Output (DIDO) Communication Systems" U.S. Application No. 12 / 802,974, entitled "System and Method For Managing Inter-Cluster Handoff Of Clients Which Traverse Multiple DIDO Clusters" U.S. Application No. 12 / 802,989, entitled "System and Method For Managing Handoff Of A Client Between Different Distributed-Input-Distributed-Output (DIDO) Networks Based On Detected Velocity Of The Client" U.S. Application No. 12 / 802,958, entitled "System and Method For Power Control and Antenna Grouping In A Distributed-Input-Distributed-Output (DIDO) Network" U.S. Application No. 12 / 802,975, entitled "System and Method For Link Adaptation In DIDO Multicarrier Systems" U.S. Application No. 12 / 802,938, entitled "System and Method For DIDO Precoding Interpolation In Multicarrier Systems" U.S. Application No. 12 / 630,627, entitled "System and Method For Distributed Antenna Wireless Communications" U.S. Patent No. 8,170,081, issued on May 1, 2012, entitled "System and Method For Adjusting DIDO Interference Cancellation Based On Signal Strength Measurements" U.S. Patent No. 8,160,121, issued on April 17, 2012, entitled "System and Method For Distributed Input-Distributed Output Wireless Communications"; U.S. Patent No. 7,885,354, issued on February 8, 2011, entitled "System and Method For Enhancing Near Vertical Incidence Skywave ("NVIS") Communication Using Space-Time Coding". U.S. Patent No. 7,711,030, issued on May 4, 2010, entitled "System and Method For Spatial-Multiplexed Tropospheric Scatter Communications"; U.S. Patent No. 7,636,381, issued on December 22, 2009, entitled "System and Method for Distributed Input Distributed Output Wireless Communication"; U.S. Patent No. 7,633,994, issued on December 15, 2009, entitled "System and Method for Distributed Input Distributed Output Wireless Communication"; U.S. Patent No. 7,599,420, issued on October 6, 2009, entitled "System and Method for Distributed Input Distributed Output Wireless Communication"; U.S. Patent No. 7,418,053, issued on August 26, 2008, entitled "System and Method for Distributed Input Distributed Output Wireless Communication"; [ ] One solution to overcome the many limitations of the aforementioned prior art is an embodiment of Distributed Input Distributed Output (DIDO) technology. DIDO technology is described in the following patents and patent applications, all of which are assigned to the assignee of this patent and are incorporated herein by reference. These patents and applications are sometimes collectively referred to herein as the "Related Patents and Applications". U.S. Application No. 13 / 633,702, entitled "Systems and Methods for wireless backhaul in distributed-input distributed-output wireless systems" U.S. Application No. 13 / 475,598, entitled "Systems and Methods to enhance spatial diversity in distributed-input distributed-output wireless systems" U.S. Application No. 13 / 233,006, entitled "System and Methods for planned evolution and obsolescence of multiuser spectrum" U.S. Application No. 13 / 232,996, entitled "Systems and Methods to Exploit Areas of Coherence in Wireless Systems" U.S. Application No. 13 / 464,648, entitled "System and Methods to Compensate for Doppler Effects in Distributed-Input Distributed Output Systems" U.S. Application No. 12 / 917,257, entitled "Systems and Methods To Coordinate Transmissions In Distributed Wireless Systems Via User Clustering" U.S. Application No. 12 / 802,988, entitled "Interference Management, Handoff, Power Control and Link Adaptation in Distributed-Input Distributed-Output (DIDO) Communication Systems" U.S. Application No. 12 / 802,974, entitled "System and Method For Managing Inter-Cluster Handoff Of Clients Which Traverse Multiple DIDO Clusters" U.S. Application No. 12 / 802,989, entitled "System and Method For Managing Handoff Of A Client Between Different Distributed-Input-Distributed-Output (DIDO) Networks Based On Detected Velocity Of The Client" U.S. Application No. 12 / 802,958, entitled "System and Method For Power Control and Antenna Grouping In A Distributed-Input-Distributed-Output (DIDO) Network" U.S. Application No. 12 / 802,975, entitled "System and Method For Link Adaptation In DIDO Multicarrier Systems" U.S. Application No. 12 / 802,938, entitled "System and Method For DIDO Precoding Interpolation In Multicarrier Systems" U.S. Application No. 12 / 630,627, entitled "System and Method For Distributed Antenna Wireless Communications" U.S. Patent No. 8,170,081, issued on May 1, 2012, entitled "System and Method For Adjusting DIDO Interference Cancellation Based On Signal Strength Measurements" U.S. Patent No. 8,160,121, issued on April 17, 2012, entitled "System and Method For Distributed Input-Distributed Output Wireless Communications"; U.S. Patent No. 7,885,354, issued on February 8, 2011, entitled "System and Method For Enhancing Near Vertical Incidence Skywave ("NVIS") Communication Using Space-Time Coding". U.S. Patent No. 7,711,030, issued on May 4, 2010, entitled "System and Method For Spatial-Multiplexed Tropospheric Scatter Communications"; U.S. Patent No. 7,636,381, issued on December 22, 2009, entitled "System and Method for Distributed Input Distributed Output Wireless Communication"; U.S. Patent No. 7,633,994, issued on December 15, 2009, entitled "System and Method for Distributed Input Distributed Output Wireless Communication"; U.S. Patent No. 7,599,420, issued on October 6, 2009, entitled "System and Method for Distributed Input Distributed Output Wireless Communication"; U.S. Patent No. 7,418,053, issued on August 26, 2008, entitled "System and Method for Distributed Input Distributed Output Wireless Communication"; To reduce the size and complexity of this patent application, certain disclosures in related patents and applications are not explicitly stated below. Please refer to the related patents and applications for a full explanation of one of the disclosures.

[0034] This invention describes a system and method for applying inter-cell multiplexing gain in wireless communication networks via spatial processing. It employs a multi-antenna system (MAS) with multiple user (MU) transmissions (a multi-user multi-antenna system or "MU-MAS"), in which multiple antennas are randomly placed. In one embodiment of the invention, the power transmitted from the multiple antennas is constrained to minimize interference at cell boundaries (as in conventional cellular systems) and inter-cell interference is eliminated using only spatial processing methods. In another embodiment of the invention, the power transmitted from the multiple antennas is not constrained to any particular power level (as long as its power transmission level falls within regulation, safety, or practical (e.g., available power, transmitter, and / or antenna specifications) limits), thereby intentionally creating higher levels of inter-cell interference across the cell to achieve inter-cell multiplexing gain and increase the capacity of the wireless communication network.

[0035] In one embodiment, the wireless communication network is as follows: [picture] [1] [and illustrations] [3] One type of cellular network, such as a cellular network based on the LTE standard, and where multiple antennas are occasionally deployed for transceivers in large or small cells. In another embodiment of the invention, the wireless communication network is not constrained to any particular cell layout and the cell boundaries can extend over a larger area, such as in [picture] [4] [To the image] [5] In. For example, a wireless communication network may be a wireless local area network (WLAN) having multiple antennas as WiFi access points, or a mesh, specific, or sensor network, or a distributed antenna system, or a DIDO system having access points placed by chance but without any transmission power constraints. However, such exemplary network structures should not be construed as limiting the general applicability of the invention to wireless communication networks. The invention is applicable to any wireless network in which multiplexing gain is achieved by transmitting signals from multiple antennas that interfere with each other when received by multiple UEs in order to form a simultaneous non-interference data stream to multiple UEs.

[0036] The MU-MAS comprises a centralized processor, a network, and M transceiver stations (or distributed antennas) for wireless communication with N user terminals or UEs. The centralized processor unit receives N data streams containing different network content intended for use on different user terminals (e.g., video, web pages, video games, text, voice, etc., streaming from web servers or other network sources). Hereafter, the term "data stream" is used to refer to any data stream transmitted over the network containing information that can be demodulated or decoded into an independent 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 data stream is a bit sequence carrying network content that can be demodulated or decoded into an independent stream.

[0037] Centralized processors utilize precoding transformations to combine N information streams from network content (according to algorithms, such as those described in related patents and applications) into M bit streams. Precoding transformations can be linear (e.g., zero-approaching

[65] , block diagonalization [66-67], matrix inversion, etc.) or non-linear (e.g., dirty paper coding [68-70] or Tomlinson-Harashima precoding [71-72], raster techniques or grid precoding [73-74], vector perturbation techniques [75-76]). Hereafter, the term "bit stream" is used to refer to any sequence of bits that may not contain any useful bits of information and therefore cannot be demodulated or decoded into a separate stream to extract network content. In one embodiment of the invention, the bit stream is a complex baseband signal generated by a centralized processor and quantized for a given number of bits to be transmitted to one of M transceiver stations.

[0038] Precoding is calculated at a centralized processor using Channel State Information (CSI) and applied to data streams multiplexed to or from multiple users on DL or UL channels. In one embodiment, the centralized processor knows the CSI between the distributed antenna and the user terminal device and uses the CSI to precode data transmitted via the DL or UL channel. In the same embodiment, the CSI is estimated at the user terminal device and fed back to the distributed antenna. In another embodiment, the DL-CSI is derived from the UL-CSI at the distributed antenna using radio frequency (RF) calibration and applying UL / DL channel reciprocity.

[0039] In one embodiment, MU-MAS is a distributed input distributed output (DIDO) system, as described in relevant patents and patent applications. In another embodiment, [picture] The MU-MAS shown in

[13] consists of the following components: ˙ [User device] [(UE)]1301: For one of the RF transceivers of a fixed and / or mobile user terminal to receive data streams via a downlink (DL) channel for self-reload transmission and to transmit data via an uplink (UL) channel for reload transmission. ˙ [Base transceiver station] [(BTS)] 1302: The BTS interfaces the return transmission with the radio channel. One embodiment of the BTS is an access point consisting of a digital-to-analog converter (DAC) / analog-to-digital converter (ADC) and an RF chain for converting baseband signals into radio frequency (RF) signals. In some cases, the BTS is a single RF transceiver equipped with a power amplifier / antenna, and the RF signal is carried to the BTS via RF over fiber technology, as described in related patents and applications. ˙ [Controller] [(CTR)] 1303: A CTR is a specific type of BTS designed for certain specialized features, such as transmitting training signals for time / frequency synchronization of the BTS and / or UE, receiving control information from / transmitting control information to the UE, receiving channel status information (CSI) or channel quality information from the UE. Any MU-MAS system may include one or more CTR stations. When multiple CTRs are available, information to or from these stations can be combined to increase diversity and improve link quality. In one embodiment, CSI is received from multiple CTRs via Maximum Ratio Combining (MRC) to improve CSI demodulation. In another embodiment, control information is transmitted from multiple CTRs via Maximum Ratio Transmission (MRT) to improve SNR at the receiver side. The scope of this invention is not limited to MRC or MRT, and any other diversity techniques (such as 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 interfaces the Internet or other types of external networks 1306 with the backhaul transport. In one embodiment, the CP calculates MU-MAS baseband processing and sends the waveform to a distributed BTS for DL ​​transport. ˙ [Base station network] [(BSN)]1305: A BSN is a network that connects a CP to a distributed BTS carrying information for DL ​​or UL channels. A BSN is a wired network, a wireless network, or a combination of both. For example, a BSN is a DSL, cable, fiber optic network, or a line-of-sight (LOS) or non-line-of-sight (NLOS) wireless link. Furthermore, a BSN is a private network, a local area network, or the Internet.

[0040] The following section explains how the aforementioned MU-MAS framework can be incorporated into the LTE standard for cellular systems (and non-cellular systems that also utilize the LTE protocol) to achieve additional gains in spectral efficiency. This begins with a general overview of the LTE framework and the modulation techniques employed in DL and UL channels. Then, a brief description of the physical layer framework structure and resource allocation within the LTE standard is provided. Finally, the LTE framework is used in a multi-user scenario to define MU-MAS precoding methods for downlink (DL) and uplink (UL) channels. For the DL scheme, two solutions are proposed: an open-loop DIDO scheme and a closed-loop DIDO scheme.

[0041] [LTE] is designed with a flat network architecture (rather than a hierarchical architecture based on the previous cellular standard) to provide: reduced latency, reduced packet loss via ARQ, reduced call setup time, and improved coverage and throughput via macro diversity. [picture] The network elements in the LTE network shown in [6] are based on

[79] : ˙ [GW] (Gateway): A router that connects the LTE network to an external network (i.e., the Internet). This GW is divided into a servo gateway that terminates the E-UTRAN interface 608 ( [S-GW]) 601 and a PDN gateway with an external network interface ( [P-GW]) 602. S-GW and P-GW are part of the so-called Evolved Packet Core (EPC) 609; ˙ [MME] (Mobility Management Entity) 603: Manages mobility, security parameters, and UE identifiers. This MME is also part of the LTE EPC; ˙ [eNodeB] (Enhanced Node B) 604: A base station responsible for radio resource management, user mobility, and scheduling; ˙ [UE] (User Equipment) 605: Mobile station. ˙ [S1] [and] [X2] [Interface] (606 and 607): Wired or wireless backhaul transmission between MME and eNodeB (S1-MME), between S-GW and eNodeB (S1-U), and between multiple eNodeBs (X2).

[0042] In one embodiment of the present invention, the MU-MAS network is an LTE network, wherein the UE is an LTE UE, the BTS is an LTE eNodeB, the CTR is an LTE eNodeB or MME, the CP is an LTE GW, and the BSN is an S1 or X1 interface. Hereafter, the terms Distributed Antenna, BTS, and eNodeB may be used interchangeably to refer to any base station in the MU-MAS, DIDO, or LTE system.

[0043] [LTE] frames have a duration of 10 ms and consist of ten sub-frames, such as [picture] [7] illustrates [33, 80]. Each subframe is divided into two time slots, each lasting 0.5 msec. The LTE standard defines two types of frames: i) Type 1 is used for FDD operations, such as in [picture] In [7a)], all subframes are assigned to either the DL channel or the UL channel; ii) Type 2 is used for TDD operations, as in [picture] In [7b)], a portion of the subframe is assigned to DL and a portion to UL (depending on the selected configuration), while several subframes are reserved for "special purposes". Each frame has at least one special subframe and consists 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.

[0044] LTE employs Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA) modulation for DL ​​and Single Carrier Frequency Division Multiple Access (SC-FDMA) for UL. The "Resource Element" (RE) is the minimum modulation structure in LTE and consists of one OFDM subcarrier in frequency and one OFDM symbol duration in time, such as... [picture] [8a] shows the DL channel and [picture] [8b] illustrates this for UL channels. A "Resource Block" (RB) consists of 12 subcarriers in the frequency and a 0.5 msec time slot (depending on the type of DL for the UL channel and the cyclic header, consisting of 3 to 7 OFDM symbol periods). The resource block for each UE is assigned on a subframe basis. Since the MU-MAS in this invention uses spatial processing to send multiple data streams to different UEs, all resource blocks can be allocated to the same UE at each subframe. In one embodiment, all or one subgroup of resource blocks are allocated to each UE and simultaneously non-interfering data streams are sent to the UE via precoding.

[0045] To establish the link between the BTS and the UE, the LTE standard defines a synchronization procedure. The BTS sends two consecutive signals to the UE: a primary synchronization signal (P-SS), transmitted via the primary synchronization channel (PSCH); and a secondary synchronization signal (S-SS), transmitted via the secondary synchronization channel (SSCH). Both signals are used by the UE for time / frequency synchronization and for retrieving the cell ID. The P-SS consists of a 63-character Zadoff-Chu sequence from which the UE derives its Entity Layer ID (0 to 2). The S-SS is one of two 31-character binary sequences interleaved and used to derive the cell ID group number (0 to 167). The UE derives the Entity Cell ID (PCI) (defined from 0 to 503) based on these two identification numbers.

[0046] 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 for forming a coherent region around the UE. In this invention, different BTSs are grouped into "antenna clusters" or "DIDO clusters," as defined in U.S. Patent No. 8,170,081, issued May 1, 2012, entitled "System and Method For Adjusting DIDO Interference Cancellation Based On Signal Strength Measurements." For example, [picture] [9] The main antenna cluster 901 and an adjacent antenna cluster 902 are shown. Each antenna cluster consists of multiple BTS 903.

[0047] In MU-MAS and DIDO systems, cell IDs can be used to distinguish antenna clusters. In one embodiment of the invention, the same cell ID is transmitted from all BTSs 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 of the invention, all BTSs within the same antenna cluster 1001 are grouped into... [picture]

[10] illustrates antenna sub-clusters 1003 with different shaded colors, and a different cell ID 1004 is associated with each antenna sub-cluster. In one embodiment, antenna sub-clusters are statically defined according to a predefined clustering plan or based on GPS positioning information. In another embodiment, antenna sub-clusters are dynamically defined based on measurements of relative signal strength between BTSs or GPS positioning information. In a different embodiment of the invention, a different cell ID is assigned to each coherent area associated with the UE (as described in U.S. Application No. 13 / 232,996, entitled "Systems and Methods to Exploit Areas of Coherence in Wireless Systems").

[0048] When all BTSs within the same antenna cluster or sub-cluster transmit LTE broadcast channels (e.g., P-SS and S-SS) to the UE, destructive interference can degrade the effectiveness of time or frequency synchronization achieved by the broadcast channels. Destructive interference can be caused by multipath propagation from spatially distributed BTSs that are incoherently reassembled at some UE locations. To avoid or mitigate this effect, in one embodiment of the invention, only one BTS within the same antenna cluster or sub-cluster transmits the LTE broadcast channels (e.g., P-SS and S-SS) to all UEs. In the same embodiment, the BTS transmitting the LTE broadcast channels is selected to maximize the power received at the UE via the broadcast channels. In another embodiment, only a limited set of BTSs is selected to transmit the LTE broadcast channels simultaneously to all UEs, thereby avoiding destructive interference at the UEs. In a different embodiment of the invention, the LTE broadcast channels are transmitted at a power higher than the payload to reach all UEs within the same antenna cluster or sub-cluster.

[0049] As explained above, advanced LTE supports carrier aggregation (CA) schemes to increase data rates on DL channels. In MU-MAS, CA can be used in conjunction with precoding to increase the data rate per user. In one embodiment of the invention, transmission precoding is applied to different portions of the RF spectrum (inter-band CA) or different frequency bands within the same portion of the spectrum (intra-band CA) to increase the data rate per user. When inter-band CA is used, the path loss at different frequency bands can be significantly altered because these frequency bands can be centered at different carrier frequencies. In conventional LTE cellular systems, frequency bands at lower carrier frequencies experience a path loss lower than those at higher carrier frequencies. Therefore, applying inter-band CA in cellular systems can lead to undesirable inter-cell interference at lower carrier frequencies. In contrast, the MU-MAS of this invention is not limited to interference at cell boundaries because BTS is distributed and does not have the concept of cells. This more flexible system layout allows for different methods of inter-band CA in MU-MAS. In one embodiment of the invention, MU-MAS achieves inter-band CA by employing one set of BTSs operating at a lower carrier frequency and another set of BTSs operating at a higher carrier frequency, such that the two sets intersect or one set is a subset of the other. In another embodiment, MU-MAS with precoding uses a CA method along with frequency hopping patterns to improve robustness against frequency-selective fading or interference. [1.] [LTE] [Middle-downlink closed loop] [MU-MAS] [Precoding Methods] [ ]

[0050] The MU-MAS closed-loop scheme can be used in time-division duplex (TDD) or frequency-division duplex (FDD) systems. In FDD systems, the DL channel and UL channel operate at different frequencies, therefore the DL channel status information (CSI) must be estimated at the UE side and reported back to the CP via the UL channel through the BTS or CTR. In TDD systems, the DL channel and UL channel are set to the same frequency, and the system can employ closed-loop technology with channel reciprocity (as described in the following sections) or an open-loop scheme. The main disadvantage of the closed-loop scheme is that it requires feedback, resulting in a larger additional item of control information on the UL.

[0051] The general mechanism of the closed-loop scheme in MU-MAS is described as follows: i) The BTS transmits signaling information to the UE via the DL; ii) The UE uses the transmitted signaling information to estimate the DL CSI from all "active BTSs"; iii) The UE quantizes the DL CSI or uses the codebook to select the precoding weights to be used for the next transmission; iv) The UE transmits the quantized CSI or codebook index to the BTS or CTR via the UL channel; v) The BTS and CTR report the CSI information or codebook index to the CP that calculates the precoding weights for data transmission on the DL. An "active BTS" is defined as a set of BTSs to which a given UE arrives. For example, in U.S. Application No. 12 / 802,974, entitled "System and Method For Managing Inter-Cluster Handoff Of Clients Which Traverse Multiple DIDO Clusters," and U.S. Application No. 12 / 917,257, entitled "Systems and Methods To Coordinate Transmissions In Distributed Wireless Systems Via User Clustering," "user cluster" 905 is defined as the group of BTSs to which a given UE arrives, such as... [picture] As illustrated in [9]. The number of active BTSs is not limited to a single user cluster in order to reduce the amount of CSI that will be estimated from the BTS to a given UE, thereby reducing the complexity of feedback add-ons on the UL and MU-MAS precoding calculations at the CP.

[0052] As explained in paragraph

[0083] , MU-MAS precoding employs either linear or nonlinear methods. In the case of nonlinear methods (e.g., dirty paper coding [68-70] or Tomlinson-Harashima precoding [71-72], grid techniques or mesh 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 account for the CSI of all UEs within the antenna cluster. Alternatively, linear precoding methods (e.g., zero-approaching

[65] , block diagonalization [66-67], matrix inversion, etc.) can be used on a user cluster basis, since the precoding weights for each UE are calculated independently of other UEs. Depending on the number of UEs and eNodeBs within the antenna cluster and user cluster, linear precoding methods offer different computational performance compared to nonlinear precoding methods. For example, if a 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*C³), while the complexity of nonlinear precoding is O(M*K²). Therefore, it is desirable to develop a method that dynamically switches between two types of precoding techniques based on the number of UEs and eNodeBs in the MU-MAS to reduce the computational complexity at the CP. In one embodiment of the invention, the MU-MAS employs a linear precoding method. In another embodiment, the MU-MAS employs a nonlinear precoding method. In the same embodiment of the 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., close to eNodeBs) and a beamforming or diversity method for UEs with poor link quality (e.g., far from eNodeBs). [1.1 LTE] [Standard downlink] [MU-MAS] [Method for sending signals] [ ]

[0053] The LTE standard defines two types of reference signals (RS) for DL ​​signaling in closed-loop schemes [33, 50, 82-83]: i) cell-specific reference signals (CRS); ii) UE-specific RS, such as channel state information (CSI) reference signals (CSI-RS) and demodulation-modulated RS (DM-RS). Cell-specific RSs are not precoded, but UE-specific RSs are precoded

[50] . CRSs are used in LTE Release 8, which employs a book-based SU / MU-MIMO technique (where each cell has up to four antennas). Advanced LTE Release 10 supports non-book-based SU / MU-MIMO schemes (where there are up to eight transmit antennas) and CoMP schemes (where there are antennas distributed across different cells). Therefore, Release 10 allows for a more flexible signaling scheme via CSI-RS. In this invention, it is explained how either type of signaling scheme can be used to achieve precoding in a MU-MAS system. [1.1.1] [use] [CRS] [Of] [MU-MAS] [Send signal] [ ]

[0054] In LTE (Version 8) systems, a CRS is used to estimate the CSI from all transmit antennas at the BTS to the UE [80, 84]. The CRS is obtained as a product of a two-dimensional orthogonal sequence and a two-dimensional pseudo-random number (PRN) sequence. For a total of 504 different CRS sequences, there are 3 orthogonal sequences (i.e., placed on several sets of orthogonal OFDM subcarriers) and 168 possible PRN sequences. Each sequence uniquely identifies a cell. Each of the three orthogonal CRSs is associated with one of the three entity layer IDs (0 to 2) that generate a different cell ID, as explained in the previous subsections. The CRS is transmitted in the first and third-to-last OFDM symbols of each time slot and every five subcarriers. Orthogonal patterns of time and frequency are designed for each transmit antenna at the BTS to enable the UE to uniquely estimate the CSI from each of the transmit antennas. Version 8 defines up to four orthogonal patterns per CRS, with one orthogonal pattern used for each of the four transmit antennas employed in MIMO 4 × 4. This high density of CRS in time and frequency (i.e., every 0.5 msec time slot and every five subcarriers) is intentionally designed to generate 5% additional time and frequency to support scenarios with rapid channel changes over time and frequency

[83] .

[0055] In version 8, since there are up to three orthogonal CRSs (or six orthogonal CRSs for a single-antenna mode) with four orthogonal patterns for each of the multi-antenna modes, up to 12 transmission antennas can be identified within the same coverage area without causing interference to the CRSs. In one embodiment of the invention, antenna cluster 1001 is divided into three antenna sub-clusters 1005, as in [picture]

[10] In this embodiment, different entity layer IDs (or cell IDs) are associated with each of the antenna subclusters, such that each antenna subcluster is assigned one of three orthogonal CRSs with four orthogonal patterns (i.e., each antenna subcluster can support up to four BTSs without causing interference to the CRS from other BTSs). In this embodiment, each cluster can support up to 12 BTSs without causing interference to the CRS.

[0056] In scenarios where more than twelve BTSs are placed within the same cluster, it is desirable to increase the number of available orthogonal CRSs to support a larger number of active BTSs (i.e., BTSs that simultaneously transmit precoded signals to the UE). One way to achieve this is to define three or more antenna sub-clusters 1003 for each antenna cluster 1101 and assign the same three entity layer IDs (or cell IDs 1104 from 0 to 2) to the antenna sub-clusters 1103 in a repeating pattern, such as... [picture] As shown in

[11] . It is observed that antenna subclusters can have different shapes and are defined in such a way that each user cluster 1102 cannot 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 the area of ​​antenna subclusters 1103 as larger than that of user clusters 1102 and to avoid adjacent antenna subclusters using the same physical layer ID. In one embodiment of the invention, multiple antenna subclusters are placed in the same antenna cluster in a repeating pattern so that the individual CRSs of the multiple antenna subclusters do not interfere with each other, thereby achieving simultaneous non-interference transmission from more than twelve BTSs.

[0057] In a practical MU-MAS system, it is possible for each UE to see more than four BTSs within its user cluster. For example, [picture]

[12] The SNR distribution of a practical deployment of a DIDO or MU-MAS system in downtown San Francisco, California is shown. The propagation model is based on the 3GPP path loss / shading model

[81] and uses a carrier frequency of 900 MHz. Points on the map indicate the location of DIDO-BTS, while black circles represent user clusters (where the UE is located at the center of the circle). In sparsely populated areas 1201, the UE can only see a few BTSs within its user cluster (e.g., for example, for [picture]

[12] In the example, there are as few as three BTSs), while in densely populated areas 1202, each user cluster may include up to 26 BTSs, such as in [picture]

[12] in.

[0058] In MU-MAS, high redundancy of the CRS can be applied so that the CSI estimate from any number of transmit antennas can be greater than four. For example, if the channel is fixed radio or characterized by low Doppler effect, there is no need to calculate the CSI from all four transmit antennas for every 0.5 ms (slot duration). Similarly, if the channel is frequency flat, the CSI estimate every five subcarriers is redundant. In that case, the resource elements (REs) occupied by the redundant CRS can be reallocated for other transmit antennas or BTSs in the MU-MAS. In one embodiment of the invention, the system allocates the resource elements of the redundant CRS to additional antennas or BTSs in the MU-MAS system. In another embodiment, the system estimates the time and frequency selectivity of the channel and dynamically allocates the CRS for different BTSs or only BTSs within a user cluster to different resource elements.

[0059] The number of BTSs included in each user cluster depends on the signal power level of all BTSs in the user cluster measured at the UE relative to the noise power level or signal-to-noise ratio (SNR). In one embodiment, the UE estimates the SNR from all BTSs in its neighborhood and selects BTSs belonging to its user cluster based on this SNR information. In another embodiment, the CP knows the SNR from the BTS to each UE (based on feedback information from the UE or information obtained from the UL channel using UL / DL channel reciprocity) and selects a set of BTSs to be included in each user cluster.

[0060] The number of BTSs included in each user cluster determines the performance of the MU-MAS method described in this invention. For example, if the number of BTSs per user cluster is low, the UE experiences higher levels of out-of-cluster interference, resulting in a high signal-to-interference-to-noise ratio (SINR) and low data rate. Similarly, if a large number of BTSs are selected for each user cluster, the SNR measured at the UE from BTSs at the edge of the user cluster is low and can be dominated by out-of-cluster interference from adjacent BTSs outside the user cluster. There exists an optimal number of BTSs per user cluster that produces the highest SINR and data rate. In one embodiment of this invention, the CP selects the optimal number of BTSs per user cluster to maximize the SINR and data rate of the UE. In another embodiment of this invention, the BTSs per user cluster are dynamically selected to adapt to changes in the propagation environment or UE mobility.

[0061] Another drawback of using a large number of BTSs per user cluster is the high computational load. In fact, the more BTSs in a user cluster, the greater the computational complexity of the MU-MAS precoder. In one embodiment of the invention, the BTSs in each user cluster are selected to achieve an optimal trade-off between SINR or data rate performance and the computational complexity of the MU-MAS precoder. In another embodiment, the BTSs in each user cluster are dynamically selected based on a trade-off between propagation conditions and the available computational resources in the MU-MAS. [1.1.2] [use] [CSI-RS] [and] [DM-RS] [Of] [MU-MAS] [Send signal] [ ]

[0062] In the Advanced LTE (Version 10) standard, the CSI-RS is used by each UE to estimate the CSI from the BTS [33, 83]. The standard defines orthogonal CSI-RS for different transmitters at the BTS so that the UE can distinguish CSI from different BTSs. The CSI-RS supports up to eight transmission antennas at the BTS, as shown in Tables 6.10.5.2-1, 2 in

[33] . The CSI-RS is transmitted at a period of between 5 and 80 subframes (i.e., the CSI-RS is transmitted every 5 to 80 ms), as shown in Table 6.10.5.3-1 in

[33] . The periodicity of the CSI-RS in Advanced LTE is intentionally designed to be greater than that of the CRS in LTE to avoid excessive additional control information, especially for traditional LTE terminals that cannot utilize such additional resources. Another reference signal used for CSI estimation is the demodulation-modulated RS (DM-RS). The DM-RS is a demodulation reference signal intended for use with a specific UE and transmitted only in a resource block assigned to the transmission to that UE.

[0063] When there are eight or more antennas (the maximum number of transmitters supported by the Advanced LTE standard) within a user cluster, alternative techniques must be employed to achieve DIDO precoding while maintaining system compliance with the Advanced LTE standard. In one embodiment of the invention, each UE uses CSI-RS or DM-RS, or a combination of both, to estimate the CSI from all active BTSs in its own user cluster. In the same embodiment, the DIDO system detects the number of BTSs in the user cluster and whether the user cluster complies with the Advanced LTE standard (supporting up to eight antennas). If it does not, the DIDO system employs alternative techniques to achieve DL transmission from the BTSs to the current UE. In one embodiment, the transmission power from the BTSs is reduced until the number of UEs in its user cluster reaches a maximum of eight BTSs. However, this solution can result in a reduction in data rate due to reduced coverage.

[0064] Another solution is to divide the BTSs in the user cluster into subgroups and send a set of CSI-RS for each subgroup at a time. For example, if the CSI-RS period is 5 subframes (i.e., 5 msec), as shown in Table 6.10.5.3-1 in

[33] , then a CSI-RS is sent every 5 msec from a new BTS subgroup. Note that this solution works as long as the CSI-RS period is short enough to cover all BTS subgroups within the UE's channel coherence time (which is a function of the UE's Doppler speed). For example, if the CSI-RS period is selected to be 5 msec and the channel coherence time is 100 msec, then it is possible to define 8 BTSs, each with up to 20 BTS subgroups, thereby adding up to a total of 160 BTSs in the user cluster. In another embodiment of the invention, the DIDO system estimates the channel coherence time of the UE and decides how many BTSs can be supported in a user cluster for a given CSI-RS periodicity to avoid degradation caused by channel changes and the Doppler effect.

[0065] All proposed solutions for CSI-RS to date are LTE compliant and deployable within the framework of conventional LTE systems. For example, proposed methods allowing more than eight antennas per user require no modifications to the UE LTE hardware and software implementation, only minor modifications to the protocols used at the BTS and CP to achieve BTS subgroup selection at any given time. These modifications can be easily implemented in a cloud-based software-defined radio (SDR) platform, a promising deployment paradigm for DIDO and MU-MAS systems. Another option is to relax the constraints of the LTE standard and develop slightly modified hardware and software for LTE UEs to support similar but non-LTE compliant DIDO or MU-MAS operating modes, enabling the UE to operate in either a fully LTE compliant mode or a modified mode supporting non-LTE DIDO or MU-MAS operation. For example, this would achieve another solution that increases the number of CSI-RS to achieve a higher number of BTSs in the system. In another embodiment of the invention, different CSI-RS patterns and periodicities are permitted as a means of increasing the number of BTSs supported per user cluster. Such minor modifications to the LTE standard can be small enough that existing LTE UE assemblies can be used with simple software modifications. Alternatively, if hardware modifications to the assemblies are required, the changes will be minor. [1.2 LTE] [Uplink within the standard] [MU-MAS CSI] [Feedback Method] [ ]

[0066] In LTE and Advanced LTE standards, the UE feeds back information to the BTS to transmit its current channel conditions and precoding weights for closed-loop transmission on the DL channel. These standards

[35] contain three different channel indicators: ˙ Rank indicator ( [RI]: Indicates how many spatial streams are transmitted to a given UE. This number is always equal to or less than the number of transmission antennas. Precoding matrix indicator ( [PMI]: This is an index used for the codebook of precoding on DL channels. Channel quality indicator ( [CQI]: Defines the modulation and forward error correction (FEC) coding schemes on the DL that will be used to maintain the performance of a predefined error rate for a given channel condition.

[0067] For the entire bandwidth report, there is only one RI, while PMI and CQI reports can be wideband or per-band depending on the channel's frequency selectivity. These indicators are transmitted in UL via two different types of physical channels: i) physical uplink control channel ( [PUCCH]), which is used only for control information; ii) channels shared by the entity's uplink ( [PUSCH] is used for both data and control information allocated within a resource block (RB) and on a subframe basis. On the PUSCH, the procedures for reporting RI, PMI, and CQI are periodic, and the indicators can be wideband (for frequency-flat channels) or selected UEs on a primary band basis (for frequency-selective channels). On the PUSCH, the feedback procedures are aperiodic and can be selected UEs on a primary band basis (for frequency-selective channels) or subbands of higher-level configurations (e.g., for transmission mode 9 in Advanced LTE with eight transmitters).

[0068] In one embodiment of the invention, the DIDO or MU-MAS system uses RI, PMI, and CQI to report its current channel conditions 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, where DIDO precoding requires a large number of indicators, the UE uses PUSCH to report additional indicators to the CP. In the case of a frequency-flat channel, the UE may apply additional UL resources to report PMI to a larger number of antennas in the DIDO system. In one embodiment of the invention, the UE, BTS, or CP estimates channel frequency selectivity, and in the case of a frequency-flat channel, the UE applies additional UL resources to report PMI to a larger number of BTSs. [2.] [LTE] [Downlink Open Loop] [MU-MAS] [Precoding Methods] [ ]

[0069] The open-loop MU-MAS precoding scheme can be used only in time-division duplex (TDD) systems employing RF calibration and channel reciprocity. The general mechanism of the open-loop scheme in MU-MAS consists of the following: i) The UE transmits signaling information to the BTS or CTR via the UL; ii) The BTS or CTR uses the transmitted signaling information to estimate the UL CSI from all UEs; iii) The BTS or CTR uses RF calibration to convert the UL CSI into DL CSI; 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 the precoding weights for data transmission on the DL. Similar to the closed-loop MU-MAS precoding scheme, user clustering can be used to reduce the amount of CSI estimated from the UE at the BTS, thereby reducing the computational burden at the BTS and the amount of signaling required on the UL. In one embodiment of the invention, open-loop precoding technology is used to transmit simultaneous, non-interfering data streams from the BTS to the UE via the DL channel.

[0070] In LTE, there are two types of reference signals used for uplink channels [31, 33, 87]: i) sounding reference signals (SRS), used for scheduling and link adaptation; ii) demodulation reference signals (DMRS), used for data reception. In one embodiment of the invention, DMRS is used in an open-loop precoding system to estimate the UL channel from all UEs to all BTSs. In the time domain, DMRS is transmitted at the fourth OFDM symbol of each LTE time slot (with a duration of 0.5 ms) (when using a normal cyclic first code). In the frequency domain, the DMRS transmitted via PUSCH is mapped for each UE to the same resource block (RB) used by the other UE for UL data transmission.

[0071] The length of the DMRS is MRS=mNRB, where m is the number of RBs and NRB=12 is the number of subcarriers per RB. To support multiple UEs, up to twelve DMRSs are generated from a basic Zadoff-Chu

[88] or computer-generated constant amplitude zero autocorrelation (CG-CAZAC) sequence via twelve 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 an OFDM symbol is 110 (i.e., using a total signal bandwidth of 20 MHz), up to 110 × 30 = 3300 different sequences may be generated. It is observed that the 30 basic sequences are not guaranteed to be orthogonal and designed to reduce cross-cell interference without completely eliminating it. In contrast, the 12 cyclic shifts of the same basic sequence are orthogonal, thereby allowing up to 12 UEs to transmit in the UL via the same RB without interference. The cyclic shift value used by each UE is provided by the BTS via Downlink Control Information (DCI) messages sent through the PDCCH. In version 8, the DCI consists of 3 bits, which allows the UE to use only up to 8 values ​​of the cyclic shift from a set of 12 possible options.

[0072] This invention employs cyclic shifting of the basic DMRS sequence to achieve a MU-MIMO scheme on the UL channel and to estimate the CSI from multiple UEs used for DL ​​precoding when channel reciprocity is applied in TDD mode. In one embodiment of the invention, an open-loop precoding method is used to transmit simultaneous non-interference data streams from a distributed BTS to the UE via the DL channel. In another embodiment of the invention, an open-loop MU-MIMO method is used to receive simultaneous non-interference data streams from the UE to the BTS via the UL channel. The same CSI estimated via the UL from all participating UEs can be used to calculate the receiver spatial filtering for MU-MIMO operation in the UL and the weights for DL ​​precoding. Since version 8 defines only a maximum of 8 orthogonal DMRS (due to the finite DCI bits, as explained above), the MU-MIMO scheme for the UL channel and the MU-MAS precoding scheme for the DL channel can support up to eight UEs, assuming all UEs utilize the full UL bandwidth.

[0073] One method to increase the number of simultaneous UEs served via MU-MIMO in UL or MU-MAS precoding in DL is through DMRS for frequency-domain multiplexed UEs. For example, if a 10MHz bandwidth is used in TDD mode, there are 50 RBs that can be allocated 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 served simultaneously. CSI is then calculated by interpolating an estimate from the DMRS transmitted via interleaved RBs. A larger number of simultaneous UEs can be supported by increasing the number of interleaved patterns of UL RBs. These patterns can be statically or dynamically assigned to different UEs based on a specific frequency hopping sequence. In one embodiment of the invention, DMRS is assigned to UEs via orthogonally interleaved RBs to increase the number of UEs that will be supported via MU-MIMO or MU-MAS precoding. In the same embodiment, interleaved RBs are statically assigned. In another embodiment, interleaved RBs are dynamically assigned according to a specific frequency hopping pattern.

[0074] An alternative solution is to multiplex DMRS for different UEs in the time domain. For example, UEs are divided into different groups and DMRS for those groups is transmitted in consecutive time slots (each with a duration of 0.5 msec). However, in this case, it is necessary to ensure that the periodicity of DMRS assignment for different groups is less than the channel coherence time of the fastest moving UE. In fact, this is a necessary condition to ensure that the time from estimating CSI via DMRS to the system transmitting the DL data stream to the UE via DIDO precoding remains unchanged for all UEs. In one embodiment of the invention, the system divides the active UEs into several groups and assigns the same set of DMRS to each group in consecutive time slots. In the same embodiment, the system estimates the shortest channel coherence time for all active UEs and calculates the maximum number of UE groups and the periodicity of DMRS time multiplexing based on that information.

[0075] Another solution involves spatially separating different groups of UEs using the same set of DMRS. For example, the same set of orthogonal DMRS can be used to identify UEs from the same cell ID. [picture]

[11] All UEs in different antenna subclusters. In one embodiment of the invention, the group space of UEs using the same set of orthogonal DMRS is spatially separated to avoid interference between groups. In the same embodiment, different antenna subclusters identified by the same cell ID use the same set of orthogonal DMRS. MU-MAS can assign UEs to "virtual cells" to maximize the number of DMRS available in the UL. In an exemplary embodiment, the virtual cell is a coherent area around the UE (described in the related application U.S. Application No. 13 / 232,996 entitled "Systems and Methods to Exploit Areas of Coherence in Wireless Systems") and the DIDO system generates up to 3300 coherent areas for different UEs. In another embodiment of the invention, each of the 30 basic sequences is assigned to a different antenna cluster (as defined in U.S. Patent No. 8,170,081, issued May 1, 2012, entitled "System and Method For Adjusting DIDO Interference Cancellation Based On Signal Strength Measurements") to reduce inter-cluster interference across adjacent antenna clusters. [3.] [LTE] [Uplink in the middle] [MU-MAS] [method] [ ]

[0076] This invention employs an open-loop MU-MIMO scheme on the UL channel to simultaneously receive UL data streams from all UEs to the BTS. The UL open-loop MU-MIMO scheme consists of the following steps: i) The UE transmits signaling information and data payload to all BTSs; ii) The BTS uses the signaling information to calculate channel estimates from all UEs; iii) The BTS transmits the channel estimates and data payload to the CP; iv) The CP uses the channel estimates 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 employs single-carrier frequency-division multiple access (SC-FDMA) to increase the number of UL channels from the UE to the BTS and to multiplex them in the frequency domain.

[0077] In one embodiment, synchronization among UEs is achieved via a signal transmitted from the DL, and all BTSs are assumed to be locked to the same time / frequency reference clock via direct connection to the same clock or (in one embodiment) via GPSDO sharing a common time / frequency reference. Variations in channel delay spread at different UEs can cause jitter in the time references of different UEs, which can affect the performance of the MU-MIMO method on the UL. In one embodiment, only UEs within the same antenna cluster (e.g., UEs closely spaced) are processed using the MU-MIMO method to reduce the relative propagation delay spread across different UEs. In another embodiment, the relative propagation delay between UEs is compensated at the UE or at the BTS to ensure simultaneous reception of data payloads from different UEs at the BTS.

[0078] The method used to transmit signaling information for data demodulation on the UL is the same method used for signaling in the downlink open-loop DIDO scheme described in previous chapters. The CP employs different spatial processing techniques to remove inter-channel interference from the UE data payload. In one embodiment of the invention, the CP employs nonlinear spatial processing methods, such as maximum likelihood (ML) receivers, decision feedback equalization (DFE) receivers, or continuous interference cancellation (SIC) receivers. In another embodiment, the CP employs linear filters (such as zero-approach (ZF) or minimum mean square error (MMSE) receivers) to eliminate co-channel interference and individually demodulate the uplink data stream. [4.] [Compared to existing] [LTE] [Network Integration] [ ]

[0079] In the United States and other parts of the world, LTE networks are already operational or in the process of being deployed and / or under development. There will be significant benefits for LTE operators if they can progressively deploy DIDO or MU-MAS capabilities into their existing or submitted deployments. In this way, they can deploy DIDO or MU-MAS in areas where they will provide the most direct benefits and progressively expand DIDO or MU-MAS capabilities to cover more of their networks. When appropriate, once they have sufficient DIDO or MU-MAS coverage in an area, they can choose to completely terminate the cell and, alternatively, completely switch to DIDO or MU-MAS, achieving much higher spectrum density at a much lower cost. Throughout this transition from cellular to DIDO or MU-MAS, LTE operators' wireless customers will no longer see a loss of service. Instead, they will only see improvements in data throughput and reliability, while operators will see cost reductions.

[0080] Several embodiments exist that will achieve the gradual integration of DIDO or MU-MAS into existing LTE networks. In all cases, the BTS used for DIDO or MU-MAS will be referred to as a DIDO-LTE BTS and will utilize one of the LTE-compatible DIDO or MU-MAS embodiments described above or as other LTE-compatible embodiments that may be developed in the future. Alternatively, the DIDO-LTE BTS will utilize a slight variant of an LTE standard (such as those described above) and will update the UE (e.g., if a software update is sufficient to modify the UE to be DIDO or MU-MAS compatible) or deploy a new generation of DIDO or MU-MAS compatible UEs. In either case, the new BTS supporting DIDO or MU-MAS within the constraints of the LTE standard or as a variant of the LTE standard will hereinafter be referred to as a DIDO-LTE BTS.

[0081] The LTE standard supports various channel bandwidths (e.g., 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz). In one embodiment, an operator may allocate new bandwidth for LTE-DIDO BTS using an existing LTE network or subdivide existing LTE spectrum (e.g., 20 MHz can be subdivided into two 10 MHz blocks) to support a conventional LTE BTS in a cellular configuration in one spectrum block and a DIDO LTE BTS in another. Effectively, this establishes two separate LTE networks, and the UE device will be configured to use one or the other network or select between them. In the case of spectrum subdivision, the spectrum may be evenly or unevenly divided between the conventional LTE network and the DIDO-LTE BTS network, with more spectrum allocated to whichever network is best utilized, given the level of cellular LTE BTS and DIDO-LTE BTS deployment and / or UE usage pattern. This segmentation can be changed as needed over time, and at any given moment, when there is a fully DIDO-LTE BTS deployed to provide the same coverage as the Cellular BTS or better coverage than the Cellular BTS, all spectrum can be allocated to the DIDO-LTE BTS and the Cellular BTS can be deactivated.

[0082] In another embodiment, a conventional cellular LTE BTS can be configured to coordinate with a DIDO-LTE BTS to share the same spectrum, but use the spectrum alternately. For example, if they share spectrum equally, each BTS network will alternately utilize a 10ms frame time, such as one 10ms frame for the cellular LTE BTS, followed by one 10ms frame for the DIDO-LTE BTS. The frame time can also be subdivided into unequal intervals. This interval division can be changed as needed over time, and at any given time, when a sufficient DIDO-LTE BTS is deployed to provide the same coverage as or better than that of the cellular BTS, all time can be allocated to the DIDO-LTE BTS, and the cellular BTS can be deactivated.

[0083] In another embodiment of the invention, DIDO or MU-MAS is used as the LOS or NLOS radio backhaul transmission to small cells in LTE and Advanced LTE networks. When small cells are deployed in an LTE network, DIDO or MU-MAS provides high-speed radio backhaul transmission to those small cells. As the demand for higher data rates increases, more small cells are added to the network until the radio network reaches a limit where no more small cells can be added to a given area without causing inter-cell interference. In the same embodiment of the invention, DIDO-LTE BTS is used to gradually replace small cells, thereby utilizing inter-cell interference to provide increased network capacity. [5. MU-MAS LTE] Scheduler [ ]

[0084] In MU-MAS, distributed antennas or BTSs simultaneously transmit precoded data streams to multiple UEs. As described in related patents and applications, the number of BTSs must be equal to or greater than the number of UEs to achieve simultaneous data transmission. In practical deployments, the number of UEs may exceed the number of BTSs. In this case, additional UEs can be selected for transmission in different time slots or frequency bands according to specific scheduling principles. The scheduler uses the channel quality information of the UEs to determine the optimal group of UEs to serve at a given time and frequency. This invention uses different scheduling methods, including proportional fair scheduler algorithms, cyclic algorithms, or greedy algorithms.

[0085] As explained in previous chapters, the LTE standard defines two parameters—CQI and SRS—to inform the scheduler about the link quality of each UE. CQI measures the quality of the DL channel and is fed back from the UE to the BTS. SRS measures the quality of the UL channel from the UE's signaling information sent to the BTS. Both indicators provide information on the UL / DL channel quality that varies over time and in the frequency domain. In FDD systems, the DL scheduler must use CQI as a performance metric because the DL and UL channel qualities can vary with different carrier frequencies. In TDD mode, DL scheduling uses CSI or SRS, or a combination of both, to perform its scheduling decisions. The same performance metrics can be used for UL scheduling. In one embodiment of the invention, the MU-MAS scheduler uses CQI and SRS as performance metrics used by the scheduling algorithm.

[0086] The MU-MAS described in this invention achieves an additional channel quality indicator not disclosed in prior art: the Spatial Selectivity Indicator (SSI), as described in related U.S. Application No. 13 / 475,598 entitled "Systems and Methods to enhance spatial diversity in distributed-input distributed-output wireless systems". The SSI can be calculated based on the CSI obtained from all UEs or from UL channels (using UL / DL channel reciprocity) via a feedback mechanism. In one embodiment of this invention, the scheduler uses the SSI as a performance metric. The SSI is one measure of the spatial diversity available in the wireless link. The SSI depends on the spatial characteristics of the BTS and the UEs. In an exemplary embodiment of this invention, the scheduler obtains the SSI from all UEs and schedules those UEs with the "optimal" SSI according to a specific scheduling criterion. If more BTSs are available compared to the functional BTS, then the user selection criteria described above are combined with the antenna selection method described in U.S. Application No. 13 / 475,598, entitled "Systems and Methods to enhance spatial diversity in distributed-input distributed-output wireless systems". In one embodiment of the present invention, the scheduler selects the optimal subgroup of BTSs and UEs based on specific scheduling criteria.

[0087] about [picture] [9] [,picture]

[10] [and illustrations]

[11] In certain scenarios, there may not be a sufficiently orthogonal signaling sequence to achieve a large number of BTSs within the same antenna cluster or antenna sub-cluster. In this case, if additional BTSs are activated to cover an area with a large number of active UEs, a certain level of interference may occur. In one embodiment of the invention, the scheduler measures the interference level between antenna clusters or antenna sub-clusters and schedules UEs to minimize the effect of mutual interference on the radio link.

[0088] This invention employs the antenna selection algorithm described in U.S. Application No. 13 / 475,598, entitled "Systems and Methods to enhance spatial diversity in distributed-input distributed-output wireless systems," to select a set of optimal active BTSs based on SSI. However, this antenna selection algorithm can require high computational complexity because MU-MAS precoding must be applied to all possible permutations of the antenna subgroups before making a decision on the optimal subgroup based on the SSI performance metric. In MU-MAS with a large number of cooperating BTSs, this computational burden can become expensive or impractical in practical deployments. Therefore, it is desirable to develop alternative techniques to reduce the number of antenna subgroups while maintaining good performance of the antenna selection method. In one embodiment of this invention, MU-MAS employs a method based on the antenna subgroup ID number, hereinafter referred to as the "antenna shuffling method." In one embodiment of the invention, the antenna shuffling method subdivides a queue containing all possible antenna subgroup IDs (i.e., all possible permutations of the active BTS for a given set of available BTSs) into different groups and assigns different priorities to those groups. These groups are defined to assign a fair chance to all subgroup IDs to be selected, but the SSI metric is calculated only for a finite number of subgroups (e.g., those with the highest priority), thereby reducing computational complexity. In an exemplary embodiment, the queue of subgroup IDs is divided into three groups, each assigned according to a different rule: i) group #1, which contains IDs with the highest priority, which are removed from the group only when a new subgroup with a higher priority is identified; ii) group #2, where a new antenna subgroup (selected from group #3) is included at each iteration of the method; iii) group #3, where antenna subgroup IDs are shuffled according to a cyclic principle. At each iteration of this method, all subgroup IDs within group #1 and group #2 are categorized based on their priority to give them the opportunity to be promoted from group #2 to group #1. SSI is calculated only for subgroups within group #1 and group #2, and the antenna selection algorithm is applied only to those subgroups. [6.] [MU-MAS LTE] [User device] [ ]

[0089] This invention comprises different designs of an LTE UE. In one embodiment, the UE is an LTE UE compatible with a precoded MU-MAS, as described above. [picture] As shown in

[13] .

[0090] In one different embodiment, UE 1401 is connected to different devices 1402 and 1403 via a first network interface 1404 (e.g., Wi-Fi, USB, Ethernet, Bluetooth, fiber optic, etc.) and to MU-MAS via a second network interface 1405, such as... [picture] As shown in

[14] . The UE in Figure 14 is equipped with two different network interfaces, each consisting of one or more antennas (but in an alternative embodiment, the first network interface 1404 may be a wired interface without antennas). The antennas of the first network interface are represented by circles, while the antennas of the second network interface are represented by triangles. In the same embodiment, the second network interface supports MU-MAS precoding, MU-MAS implemented with an LTE-compliant protocol or MU-MAS (implemented with or without an LTE-compliant protocol), 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 works with either and / or both of the MU-MAS and / or the alternative network, and the UE selects the MU-MAS or the alternative network based on certain criteria. In the same embodiment, the criteria are: i) whether only one network is available and selected; ii) whether a network has better performance; iii) whether a network is more economical; iv) whether a network is less congested; and v) whether a network uses fewer UE resources.

[0091] In one embodiment of the present invention, the UE 1501 is located in a housing that is physically attached to the user device 1502, such as [picture] As illustrated in

[15] . In the same embodiment, the housing serves as a decorative addition to one of the user devices. In another embodiment, the housing is used to protect the user device from physical damage. The UE consists of a battery 1503 and one or more network interfaces 1504.

[0092] In one embodiment, the UE electronics are embedded within a housing. In the same embodiment, the UE electronics include a battery 1503. The battery includes a charger coupled via a physical electrical contact or a wireless contact. Exemplary power coupling can be conductive, inductive, RF, optical, or thermal, but power coupling is not limited to these methods. In the same embodiment, the UE electronics are coupled to receive power from a user device. This power coupling is via a physical contact or via an inductive or wireless contact. In the same embodiment, the user device is coupled to receive power from a MU-MAS UE. This coupling is via a physical contact or via an inductive or wireless contact. In a different embodiment, the same charger powers both the user device and the MU-MAS UE.

[0093] In one embodiment of the invention, the UE is configured to communicate with a user device. In the same embodiment, the UE can be reset (e.g., via a switch or by removing power) so that the user device can connect to it first, and once the connection is established, the UE can be configured by the user device. This configuration includes configuring a private password and / or other security protocols. In a different embodiment, the UE includes a component that will be configured to communicate with the user device. This configuration is accomplished via: a communication port of another device, wherein the communication port is USB; or controls and / or buttons on the UE; or a display, wherein button or touch input is used.

[0094] In another embodiment, the same RF chain is used for both MU-MAS communication and the alternative network. In yet another embodiment, a different RF chain is used for both MU-MAS communication and the alternative network. [7.] [Application Channel: Interchangeable Radio Frequency] [(RF)] [calibration] [ ]

[0095] The conventional closed-loop MU-MAS method uses UL channels to feed back quantized CSI or code indexes (as in codebook-based limited feedback schemes) from the UE to the BTS or CP. However, this scheme introduces large feedback surcharges and high protocol complexity to achieve CSI feedback channels. In TDD systems, with UL and DL set to the same frequency, it is desirable to avoid CSI feedback by applying UL / DL channel reciprocity. In practical systems, the transmit and receive RF chains at the BTS or UE typically have different characteristics due to different RF components and circuit layouts. Therefore, to maintain UL / DL reciprocity, RF calibration methods are needed to compensate for RF mismatches between the transmit and receive chains.

[0096]

[91] describes a model of RF mismatch in typical wireless transceivers, and

[92] discusses hardware solutions to mitigate the effects of RF mismatch on the performance of adaptive digital beamforming systems. Software techniques are used to achieve RF calibration in multiple-input multiple-output (MIMO) systems (proposed in [93, 94]) and experimental results for multiple-input single-output (MISO) systems and systems employing antenna selection (shown in

[95] and

[96] respectively).

[0097] However, prior art assumes that all RF chains are arranged on the same circuit board as in a MIMO system, thereby simplifying the RF calibration problem because information about RF mismatches between all RF chains can be obtained locally. In contrast, the present invention consists of geographically dispersed distributed antennas, so that communication between these antennas occurs only through the network. Therefore, a novel system unit called a "beacon station" is defined, specifically designed to achieve RF calibration in a MU-MAS with distributed antennas. Furthermore, in prior art MIMO systems, significant RF coupling occurs between the transmission / receive chains due to the close proximity of the RF chains on the same board. In contrast, in the present invention, RF coupling occurs only between one transmission chain and one receive chain of the same distributed antenna. Therefore, the technique used for RF calibration is significantly different from that described in the prior art, as will be demonstrated later. Finally, the RF calibration methods disclosed in the prior art are not limited to systems with a single user (e.g., a single user equipment device). As shown in the derivation below, systems with multiple users (e.g., MU-MAS) are particularly sensitive to RF mismatch due to the inter-user interference it generates. Therefore, special techniques must be employed to achieve RF calibration when applying channel interleaving, as explained below.

[0098] This invention comprises a MU-MAS that employs radio frequency (RF) calibration and applies one of the reciprocities between downlink (DL) and uplink (UL) channels. The MU-MAS consists of multiple distributed antennas, multiple user equipment (UE) devices, and one or more beacon stations. In one embodiment, RF calibration is used to estimate the DL MU-MAS precoding weights from the UL channel. [picture]

[16] A block diagram showing a system including a distributed antenna 1601, multiple UEs 1613, a beacon station 1619, a base station network (BSN) 1607 connecting the distributed antenna, a centralized processor (CP) 1621, and a feedback channel 1620 for the calibration control channel from the beacon station to the CP.

[0099] Each distributed antenna unit comprises a baseband unit 1602, a transmit RF chain 1603, a receive RF chain 1604, an RF switching unit 1605 that dynamically selects the transmit / receive RF chain for TDD operation, and an antenna 1606. In one embodiment, the baseband unit includes baseband signal processing and a digital-to-analog converter (DAC). In another embodiment, all baseband processing is performed at the CP to transmit RF signals to each distributed antenna (e.g., via an RF network over RF coaxial cable or fiber optic cable). Each UE comprises a baseband unit 1608, transmit RF chains 1609 and 1610 respectively, an RF switch 1611, and an antenna 1612. The beacon station comprises a baseband unit 1614, transmit RF chains 1615 and 1616 respectively, an RF switch 1617, and an antenna 1618.

[0100] The wireless link between the distributed antenna and the UE is modeled as a complex Gaussian channel matrix of size M × N. [H], where M represents the number of UEs and N represents the number of distributed antennas. [H] DL is defined as a DL channel matrix of 1622 and will [H] UL is defined as UL channel matrix 1623. Channel reciprocity is maintained as long as DL and UL are set to the same carrier frequency. In this case, the following properties are maintained. Among the symbols This indicates the transpose operation.

[0101] The above model applies to single-carrier or multi-carrier systems. In multi-carrier systems (e.g., OFDM), complex matrices... [H] represents the channel of a subcarrier, and the same model extends to any subcarrier in the system. [picture]

[16] It also demonstrates a modeled complex channel matrix with dimensions N × N. [A] T and The transmitting RF unit and receiving RF unit at the distributed antenna of [A] R. Similarly, the transmitting RF unit and receiving RF unit at the UE are respectively matrices of size M × M. [B] T and [B] R is used for modeling. In the case of a MU-MAS with distributed antennas, the RF coupling between the distributed antennas and / or the UE can be ignored due to the relative separation of the antennas, so that... [A] T、 [A] R、 [B] T and [B] R represents a diagonal matrix. It is observed that this exhibits a unique characteristic of MU-MAS, which features distributed antennas and distributed UEs. Therefore, this invention is novel compared to prior art related to multiple-input multiple-output (MIMO) systems.

[0102] based on [picture]

[16] The block diagram in which the effective DL channel matrix (modeled transmit / receive RF units and wireless links) is written as And the effective UL channel matrix is ​​written as In this invention, the RF calibration system utilizes a complex RF calibration matrix. [C] Pre-adjusted UL channel estimation matrix And obtained as follows: [ ] In one embodiment of the present invention, which includes an LTE cellular network, the effective UL channel is estimated at the eNodeB using DMRS from all UEs. like [picture] As shown in

[17] , the effective DL (Delta) between each distributed antenna 1701 and beacon station 1719 (Delta) Channel 1722 and UL ( Channel 1723 vector and matrix calculation [C], defined as and in As row vectors, it is assumed that there is DL and UL channel reciprocity between the distributed antennas and the beacon station. In one embodiment, the DL channel between the distributed antennas and the beacon station is estimated by transmitting a training signal from the distributed antennas to the beacon station. In an exemplary embodiment including an LTE cellular network, the beacon station uses DL sequence CRS, CSI-RS, or DM-RS to estimate the effective DL channel from all eNodeBs. In the same embodiment, the UL channel between the beacon station and the distributed antennas is estimated by transmitting a training signal from the beacon station to the antennas. In one embodiment of the invention, multiple beacon stations are used to improve the estimation of the RF calibration matrix. In this invention, there is no RF coupling between the distributed antennas, so that the RF calibration matrix... [C] is diagonal.

[0103] When linear precoding is used (e.g., zero-approaching

[65] , block diagonalization or BD [66-67], matrix inversion, etc.), the symbol received at the m-th UE is given as follows in System effective channel matrix The mth column, It is from The precoding vector of the m-th UE is derived. The symbol transmitted to the m-th UE, and This refers to the white Gaussian noise at the m-th UE. For simplicity, the above model uses a single receiving antenna at each UE, but the invention extends to any number of antennas at the UE. It may be demonstrated that when using the RF calibration method described above, inter-user interference at each UE can be pre-eliminated at the transmitter to maintain the following conditions. in This is a channel matrix that has undergone RF calibration. The derived precoding weight vector. In one embodiment, the precoding weights are calculated from the RF-calibrated channel matrix to pre-eliminate inter-user interference at each UE. [picture]

[18] The symbol error rate (SER) performance of MU-MAS with BD precoding and 4-QAM modulation in frequency-flat channels is demonstrated for three scenarios: i) no RF mismatch; ii) RF mismatch without calibration; iii) RF mismatch with calibration. It is observed that the RF calibration method in this invention reduces the SER to the ideal performance (i.e., no RF mismatch).

[0104] In another embodiment of the invention, a nonlinear precoding method (e.g., dirty paper coding [68-70], or Tomlinson-Harashima precoding or THP [71-72], grid technology or mesh precoding [73-74], vector perturbation technology [75-76]) is applied to an RF-calibrated channel matrix to pre-eliminate inter-user interference at each UE. [picture]

[19] Demonstrates the performance of SER and UL / DL reciprocal matching linear precoding obtained by using RF calibration with nonlinear precoding techniques. [picture] [20a] shows the constellation diagram of a MU-MAS with two distributed antennas and two UEs before the THP mode operation for UE 1, and the diagram... [20b] A constellation diagram (THP grid structure) is shown in a MU-MAS with two distributed antennas and two UEs before the THP mode operation for UE 2. THP precoding is designed to completely eliminate interference to the "reference UE" and apply the continuous interference cancellation scheme to the other UEs. Therefore, the SER performance of the reference UE is expected to be better than that of the other UEs. In one embodiment, cyclic or proportional fair scheduling or other types of scheduling techniques are applied to the UEs to ensure similar average SER performance for all UEs.

[0105] The computational performance of BD and THP methods can vary depending on the number of distributed antennas and / or UEs within each user cluster. In one embodiment of the invention, MU-MAS dynamically switches between linear and nonlinear precoding techniques depending on the number of distributed antennas and / or UEs in each user cluster to minimize the computational complexity of the precoder.

[0106] In a practical MU-MAS, the beacon station is a wireless transceiver specifically used for RF calibration. Because the beacon station needs to transmit feedback channels from all distributed antennas' estimated effective DL channels for calibration purposes, it is transmitted to the CP via a wireless or wired link. In another embodiment, the beacon station is any of the distributed antennas, and calibration parameters are calculated relative to that antenna. In the same embodiment, the distributed antennas are organized in a mesh network, and pairwise RF calibrations are calculated between adjacent distributed antennas to ensure good link quality. RF calibration is performed across all antennas, and calibration information is fed back to the CP so that all distributed antennas are calibrated to each other. In another embodiment, the beacon station is any of the UEs that use any wireless or wired link to feed calibration information back to the CP.

[0107] The calibration information sent to the CP is quantized for a limited number of bits or transmitted via a codebook-based limited feedback method to reduce additional items on the control channel. It has been observed that RF calibration can operate at a slow rate (depending on the rate of change of RF characteristics due to factors such as temperature variations). If the update rate of the calibration information is low, the radio data channel can be used to send that information to the CP without causing any significant loss of data rate. In an exemplary embodiment, in an LTE cellular network, the PUSCH is used to feed calibration information from the UE to the CP.

[0108] Each user cluster, antenna cluster, or antenna sub-cluster employs one or more geographically distributed beacons depending on the relative link quality between the beacon stations and distributed antennas within that cluster. In one embodiment, the beacon station with the best signal quality to all distributed antennas in the cluster is used for RF calibration. In another embodiment, beacons are dynamically selected at each time step to adapt to changes in link quality to the distributed antennas due to variations in the propagation environment. In yet another embodiment, multiple beacons are used collaboratively (e.g., via maximum ratio combining / transmission) to maximize the SNR or SINR on the link to / from the distributed antennas. In a different embodiment, one or more RF calibrations are performed per cluster.

[0109] In one embodiment of the invention, the beacon station is used not only for RF calibration but also for transmitting signaling information, including time and frequency synchronization references, to distributed antennas and / or UEs. The distributed antennas and / or UEs use this reference to maintain time and frequency synchronization with the MU-MAS master reference clock. In one embodiment, this reference clock distribution from the beacon station to the distributed antennas and UEs is achieved via an LTE Multimedia Broadcast Single Frequency Network (MBSFN) communication channel. [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 [2] D. Gesbert, M. Shafi, D. Shiu, PJ 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, No. 3, pp. 281-302, April 2003 [3] L. Zheng and DNC Tse, "Diversity and multiplexing: a fundamental tradeoff in multiple-antenna channels", IEEE Trans. Info. Th., Vol. 49, No. 5, pp. 1073-1096, May 2003 [4] DNC Tse, P. Viswanath and L. Zheng, "Diversity-multiplexing tradeoff in multiple-access channels", IEEE Trans. Info. Th., Vol. 50, No. 9, pp. 1859-1874, September 2004 [5] E. Visotsky and U. Madhow, “Space-time transmit precoding with perfect feedback”, IEEE Trans. Info. Th., Vol. 47, pp. 2632-2639, September 2001. [6] SA 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, June 2001. [7] SA 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. [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, September 2004. [9] AL Moustakas and SH Simon, "Optimizing multiple-input single-output (MISO) communication systems with general Gaussian channels: nontrivial covariance and nonzero mean", IEEE Trans. Info. Th., Volume 49, Pages 2770-2780, October 2003.

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[0110] 101: Multiple Work Zones 102: Episode Section 103: Large residential area 104: Small residential area 105: Base transceiver station 106: Cheap Access Point 301: Interference Zone 302: Large residential area 401: Base Transceiver Station 402: Residential Area 501: Distributed Base Transceiver Station 502: Additional Access Point 503: Community 601: Servo Gateway 602: PDN Gateway 603: Action Management Entity 604: Enhanced Node B 605: User Equipment 606:S1 Interface 607:X2 Interface 608: E-UTRAN Interface 609: Evolved Packet Core 901: Main Antenna Cluster 902: Adjacent Antenna Cluster 903: Base Transceiver Station 905: User Cluster 1001: Antenna Cluster 1003: Antenna Cluster 1004: Community ID 1101: Antenna Cluster 1102: User Cluster 1103: Antenna Cluster 1104: Community ID 1201: Sparsely populated areas 1202: Densely populated area 1301: User Equipment 1302: Base transceiver station 1303: Controller 1304: Centralized Processor 1305: Base Station Network 1306: External Network 1401: User Equipment 1402: Device 1403: Device 1404: First Network Interface 1405: Second Network Interface 1501: User Equipment 1502: User Device 1503: Battery 1504: Network Interface 1601: Distributed Antenna 1602: Baseband Unit 1603: Transmission RF Chain 1604: Receiver RF Chain 1605: Radio Frequency Switching Unit 1606: Antenna 1607: Base Station Network 1608: Baseband Unit 1609: Transmission RF Chain 1610: Receiver RF Chain 1611: Radio Frequency Switcher 1612: Antenna 1613: User Equipment 1614: Fundamental frequency unit 1615: Transmission RF Chain 1616: Receiver RF Chain 1617: Radio Frequency Switcher 1618: Antenna 1619: Beacon Tower 1620: Feedback Channel 1621: Centralized Processor 1622: Downlink Channel Matrix 1623: Uplink Channel Matrix 1701: Distributed Antenna 1719: Beacon Tower 1722: Effective downlink ( ) channel 1723: Effective uplink ( ) channel AR1: Complex Channel Matrix / Diagonal Matrix ARN: Complex Channel Matrix / Diagonal Matrix AT1: Complex Channel Matrix / Diagonal Matrix ATN: Complex Channel Matrix / Diagonal Matrix BR1: Matrix / Diagonal Matrix BRM: Matrix / Diagonal Matrix BT1: Matrix / Diagonal Matrix BTM: Matrix / Diagonal Matrix

Claims

1. A wireless communication system, comprising: A plurality of antennas, more than eight; A plurality of radio frequency (RF) transceivers, each of a plurality of antennas coupled to a corresponding one of the plurality of RF transceivers; and a processor coupled to the plurality of RF transceivers and configured to perform baseband processing, wherein the system is configured to: (1) receive, at the plurality of antennas, signaling information on an uplink (UL) from a plurality of user equipments (UEs), the signaling information comprising a plurality of reference signals generated by a plurality of cyclic shifts of a base sequence, the base sequence being a Zadoff-Chu sequence or a computer-generated constant amplitude zero autocorrelation (CG-CAZAC) sequence; (2) estimate a plurality of uplink (UL) channel state information (CSI) values ​​from the plurality of reference signals using the signaling information; (3) (3) Using uplink (UL) and downlink (DL) channel reciprocity and employing radio frequency (RF) calibration, the plurality of uplink (UL) CSI estimates are converted into a matrix of downlink (DL) CSI estimates; (4) By means of the processor, the plurality of data streams are precoded using the downlink (DL) CSI estimate matrix to generate a plurality of complex baseband signals for orthogonal frequency division multiplexing (OFDM) transmission; (5) By means of the plurality of radio frequency (RF) transceivers, the plurality of complex baseband signals are converted into a plurality of radio frequency (RF) downlink (DL) signals, wherein each of the plurality of RF transceivers converts one of the plurality of complex baseband signals into one of the plurality of RF downlink (DL) signals; and (6) The plurality of radio frequency (RF) downlink (DL) signals are transmitted from the plurality of antennas and interfere with each other at the locations where they are received by the plurality of user equipments (UEs) to create simultaneous non-interference data streams to the plurality of user equipments (UEs), thereby achieving multiplexing gain.

2. The system of claim 1, wherein one or more of the plurality of uplink (UL) transmissions include a sounding reference signal (SRS).

3. The system of claim 1, wherein the system is further configured to receive a plurality of uplink (UL) data payloads, and inter-channel interference is removed from the plurality of uplink (UL) data payloads by spatial filtering using the plurality of uplink (UL) CSI estimates.

4. The system of request item 1, wherein one or more of the plurality of uplink (UL) transmissions includes a demodulation reference signal (DMRS).

5. A method implemented in a wireless communication system, the wireless communication system comprising a plurality of antennas (more than eight), a plurality of radio frequency (RF) transceivers, and a processor, wherein each of the plurality of antennas is coupled to a corresponding one of the plurality of RF transceivers, and the processor is coupled to and configured to perform baseband processing, the method comprising: (1) At the plurality of antennas, transmit signal information on an uplink (UL) is received from a plurality of user equipments (UEs), the transmit signal information comprising a plurality of reference signals generated by multiple cyclic shifts of a basic sequence, the basic sequence being either a Zadoff-Chu sequence or a computer-generated constant amplitude zero autocorrelation (CG-CAZAC) sequence; (2) The transmit signal information is used to estimate a plurality of uplink (UL) CSI estimates from the plurality of reference signals; (3) The plurality of uplink (UL) CSI estimates are converted into a downlink (DL) CSI estimate matrix by using uplink (UL) and downlink (DL) channel reciprocity and employing radio frequency (RF) calibration; (4) The downlink (DL) CSI estimate matrix is ​​used by the processor to precode a plurality of data streams to generate a plurality of complex baseband signals for orthogonal frequency division multiplexing (OFDM) transmission; (5) The plurality of radio frequency (RF) transceivers convert the plurality of complex baseband signals into a plurality of radio frequency (RF) downlink (DL) signals, wherein each of the plurality of RF transceivers converts one of the plurality of complex baseband signals into one of the plurality of RF downlink (DL) signals; and (6) transmit the plurality of radio frequency (RF) downlink (DL) signals from the plurality of antennas, wherein the plurality of radio frequency (RF) downlink (DL) signals interfere with each other at the location where they are received by the plurality of user equipments (UEs) to create simultaneous non-interference data streams to the plurality of user equipments (UEs), thereby achieving multiplexing gain.

6. The method of claim 5, wherein one or more of the plurality of uplink (UL) transmissions includes a sounding reference signal (SRS).

7. The method of claim 5 further includes receiving a plurality of uplink (UL) data payloads and removing inter-channel interference from the plurality of uplink (UL) data payloads by spatial filtering using the plurality of uplink (UL) CSI estimates.

8. The method of claim 5, wherein one or more of the plurality of uplink (UL) transmissions includes a demodulation reference signal (DMRS).

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