Systems and methods for exploiting inter-cell multiplexing gain in wireless cellular systems via distributed input distributed output technology

Abstract

This invention describes a system and method for achieving multiplexing gain by utilizing inter-cell interference in a multi-antenna system (MAS) ("MU-MAS") with multiple user (MU) transmissions. For example, one embodiment of the MU-MAS includes a wireless cellular network having multiple distributed antennas that cooperate to cancel inter-cell interference and increase network capacity by utilizing inter-cell multiplexing gain.

Description

Technical Field

[0001] This invention relates to a communication system and a communication method, particularly to a multi-antenna system (MAS) with multi-user (MU) transmission ("MU-MAS") and a method for implementing a MU-MAS. Prior Technology

[0002] Over the past three decades, the wireless cellular market has witnessed a global increase in the number of users and a growing demand for better services, shifting from voice to web browsing and real-time HD video streaming. This increasing demand for services requiring higher data rates, lower latency, and improved reliability has driven a fundamental evolution of wireless technology through various standards. From the first-generation analog AMPS and TACS (for voice services) in the early 1980s to the 2G and 2.5G digital GSM, IS-95, and GPRS (for voice and data services) in the 1990s to the 3G with UMTS and CDMA2000 (for web browsing) in the early 21st century, and finally to the current Long Term Evolution (LTE) (for high-speed internet connectivity) 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 wireless systems. LTE achieves up to 4x improvement in downlink spectral efficiency compared to previous 3G and HSPA+ standards by utilizing the spatial components of radio channels through Multiple-Input Multiple-Output (MIMO) technology. LTE Upgrade is an evolution of LTE, currently under standardization and poised to achieve up to 8x improvement in spectral efficiency compared to 3G standard systems.

[0004] Despite this technological evolution, due to increased market penetration of smartphones and consoles, and the availability of more data-intensive applications such as real-time HD video streaming, video conferencing, and gaming, wireless carriers are likely to be unable to meet the growing demand for data rates within the next three years. It is estimated that wireless network capacity in Europe will grow by 5× from 2011 to 2015, thanks to improved technologies such as LTE and the government making more spectrum available.

[25] For example, the FCC plans to make 500 MHz of spectrum available by 2020 (of which 300 MHz will be available by 2015) to promote wireless internet connectivity throughout the United States as part of the National Broadband Initiative.

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

[25] A similar spectrum shortage is expected in the United States by 2014.[26-27] Due to this data crisis, revenue from wireless carriers will be reduced to below their CAPEX and OPEX levels and could have a potentially disruptive impact on the wireless market.

[28]

[0005] The only predictable solution to prevent this impending spectrum crisis is to promote new wireless technologies, given the insufficient capacity gains and increased spectrum availability provided by LTE deployments.

[29] LTE upgrades (evolutions of the LTE standard) promise 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 to allow for cross-cell coordination. Summary of the Invention

[0006] According to a first embodiment of the present invention, the present invention relates to a multi-antenna system (MAS) with multi-user (MU) transmission ("MU-MAS"), comprising: a plurality of antenna or radio transceiver devices (BTS) distributed over a coverage area of ​​large, non-overlaying macrocells at the same frequency, all sharing the same cell ID; a plurality of radio user devices (UEs) communicatively coupled to the plurality of radio transceiver devices (BTS); and a spatial processing unit employing precoding to generate a plurality of waveforms for the plurality of radio transceiver devices that interfere with each other, thereby creating simultaneously non-interfering downlink (DL) or uplink (UL) data links, including multiple control channel links in the same frequency band between the plurality of radio transceiver devices (BTS) and the user devices (UEs).

[0007] According to a second embodiment of the present invention, the present invention relates to a method implemented in a MU-MAS, the method comprising: distributing a plurality of radio transceiver devices (BTSs) across a coverage area of ​​large cells without cell overlap at the same frequency, all sharing the same cell ID; communicatively coupling a plurality of user equipment (UEs) to the plurality of radio transceiver devices (BTSs); and employing precoding to generate a plurality of waveforms for the plurality of radio transceiver devices that interfere with each other, thereby creating simultaneously non-interfering downlink (DL) or uplink (UL) data links, including multiple control channel links in the same frequency band between the plurality of radio transceiver devices (BTSs) and the user equipment (UEs). Simple Explanation of the Diagram

[0008] The patent or application file contains at least one drawing rendered in color. Upon request and payment of the necessary fees, the U.S. Patent and Trademark Office will provide a copy of the patent or patent publication containing the (some) colored drawings.

[0009] One aspect of the invention will be better understood from the following detailed description taken in conjunction with the drawings, wherein:

[0010] Figure 1 illustrates a small cell divided into a multi-functional region and a diversity region;

[0011] Figure 2 illustrates inter-cell interference in a plurality of different regions;

[0012] Figure 3 illustrates an embodiment in which increased power from three base transceiver stations (BTSs) transmitting simultaneously at the same frequency allows for interference at a higher level across the cell;

[0013] Figure 4 illustrates one embodiment in which numerous additional access points are added to intentionally increase the level of non-coherent interference across the cell;

[0014] Figure 5 illustrates a plurality of LTE network elements employed in one embodiment of the present invention;

[0015] Figures 6a to 6c illustrate the details associated with the LTE frame;

[0016] Figures 7a and 7b illustrate the smallest modulation structure in LTE, consisting of a frequency-based OFDM subcarrier and a time-based OFDM symbol duration, forming a "resource element".

[0017] Figure 8 illustrates the SNR distribution of an actual deployment of one embodiment of the present invention in downtown San Francisco, California;

[0018] Figure 9 illustrates a system architecture employed in one embodiment of the present invention. Implementation

[0019] [Cross-reference to related applications] [ ] This application claims the benefit of U.S. Provisional Application No. 61 / 729,990, filed November 26, 2012, entitled "Systems and Methods For Exploiting Inter-Cell Multiplexing Gain In Wireless Cellular Systems Via Distributed Input Distributed Output Technology," which has been assigned to the assignee of this application. The entire contents of this application are incorporated herein by reference. [Related Applications]

[0020] This application may relate to the following concurrently filed U.S. patent applications:

[0021] U.S. Patent Application No. 13 / 233,006, entitled "System and Methods for planned evolution and obsolescence of multiuser spectrum"

[0022] U.S. Patent Application No. 13 / 232,996, entitled "Systems and Methods to Exploit Areas of Coherence in Wireless Systems"

[0023] U.S. Patent Application No. 13 / 464,648, entitled "System and Methods to Compensate for Doppler Effects in Distributed-Input Distributed Output Systems"

[0024] U.S. Patent No. 8,542,763, issued on September 24, 2013, entitled "Systems and Methods To Coordinate Transmissions In Distributed Wireless Systems Via User Clustering"

[0025] U.S. Patent Application No. 12 / 802,988, entitled "Interference Management, Handoff, Power Control and Link Adaptation in Distributed-Input Distributed-Output (DIDO) Communication Systems"

[0026] 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"

[0027] U.S. Patent Application No. 12 / 802,974, entitled "System and Method For Managing Inter-Cluster Handoff Of Clients Which Traverse Multiple DIDO Clusters"

[0028] U.S. Patent 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"

[0029] 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"

[0030] U.S. Patent Application No. 12 / 802,975 entitled "System and Method For Link Adaptation In DIDO Multicarrier Systems"

[0031] U.S. Patent No. 8,571,086, issued on October 29, 2013, entitled "System and Method For DIDO Precoding Interpolation In Multicarrier Systems"

[0032] U.S. Application No. 12 / 630,627 entitled "System and Method For Distributed Antenna Wireless Communications"

[0033] U.S. Patent No. 7,599,420, entitled "System and Method for Distributed Input Distributed Output Wireless Communication," was granted on October 6, 2009.

[0034] U.S. Patent No. 7,633,994, issued on December 15, 2009, entitled "System and Method for Distributed Input Distributed Output Wireless Communication";

[0035] U.S. Patent No. 7,636,381, issued on December 22, 2009, entitled "System and Method for Distributed Input Distributed Output Wireless Communication";

[0036] U.S. Patent No. 8,160,121, entitled "System and Method For Distributed Input-Distributed Output Wireless Communications," was granted on April 17, 2012.

[0037] U.S. Patent No. 7,711,030, issued on May 4, 2010, entitled "System and Method For Spatial-Multiplexed Tropospheric Scatter Communications";

[0038] U.S. Patent No. 7,418,053, entitled "System and Method for Distributed Input Distributed Output Wireless Communication," was granted on August 26, 2008.

[0039] 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."

[0040] One solution to overcome many of the limitations of the prior art described above is an embodiment of Distributed Input Distributed Output (DIDO) technology. DIDO technology is described in the following patents and patent applications, which are assigned to the assignee of this invention and are incorporated herein by reference. These patents and applications are sometimes collectively referred to as the "Related Patents and Applications".

[0041] U.S. Patent Application No. 13 / 233,006, entitled "System and Methods for planned evolution and obsolescence of multiuser spectrum"

[0042] U.S. Patent Application No. 13 / 232,996, entitled "Systems and Methods to Exploit Areas of Coherence in Wireless Systems"

[0043] U.S. Patent Application No. 13 / 475,598, entitled "Systems and Methods to Enhance Spatial Diversity in Distributed Input Distributed Output Wireless Systems".

[0044] U.S. Patent Application No. 13 / 464,648, entitled "System and Methods to Compensate for Doppler Effects in Distributed-Input Distributed Output Systems."

[0045] U.S. Patent No. 8,542,763, issued on September 24, 2013, entitled "Systems and Methods To Coordinate Transmissions In Distributed Wireless Systems Via User Clustering"

[0046] U.S. Patent Application No. 12 / 802,988, entitled "Interference Management, Handoff, Power Control and Link Adaptation in Distributed-Input Distributed-Output (DIDO) Communication Systems"

[0047] 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"

[0048] U.S. Patent Application No. 12 / 802,974, entitled "System and Method For Managing Inter-Cluster Handoff Of Clients Which Traverse Multiple DIDO Clusters"

[0049] U.S. Patent 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"

[0050] 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"

[0051] U.S. Patent Application No. 12 / 802,975 entitled "System and Method For Link Adaptation In DIDO Multicarrier Systems"

[0052] U.S. Patent No. 8,571,086, issued on October 29, 2013, entitled "System and Method For DIDO Precoding Interpolation In Multicarrier Systems"

[0053] U.S. Application No. 12 / 630,627 entitled "System and Method For Distributed Antenna Wireless Communications"

[0054] U.S. Patent No. 7,599,420, entitled "System and Method for Distributed Input Distributed Output Wireless Communication," was granted on October 6, 2009.

[0055] U.S. Patent No. 7,633,994, issued on December 15, 2009, entitled "System and Method for Distributed Input Distributed Output Wireless Communication";

[0056] U.S. Patent No. 7,636,381, issued on December 22, 2009, entitled "System and Method for Distributed Input Distributed Output Wireless Communication";

[0057] U.S. Patent No. 8,160,121, entitled "System and Method For Distributed Input-Distributed Output Wireless Communications," was granted on April 17, 2012.

[0058] U.S. Patent No. 7,711,030, issued on May 4, 2010, entitled "System and Method For Spatial-Multiplexed Tropospheric Scatter Communications";

[0059] U.S. Patent No. 7,418,053, entitled "System and Method for Distributed Input Distributed Output Wireless Communication," was granted on August 26, 2008.

[0060] 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."

[0061] To reduce the size and complexity of this patent application, some disclosures of related patents and applications are not explicitly presented below. For a complete description of this invention, please refer to the relevant patents and applications.

[0062] One promising technology that will provide several orders of magnitude increase in spectral efficiency via wireless links without the limitations of conventional cellular systems is Distributed Input Distributed Output (DIDO) technology (see related patents and applications referenced above in [0002-0020]). This invention describes DIDO technologies (such as LTE or LTE-Upgrades) employed in the context of cellular systems to provide significant performance benefits over conventional wireless systems (both within and outside the constraints of cellular standards). We begin with an overview of MIMO and examine the different spatial processing techniques employed by LTE and LTE-Upgrades. We then demonstrate how this invention provides significant capacity gains for next-generation wireless communication systems compared to prior art methods.

[0063] MIMO employs multiple antennas on both the transmitter and receiver sides of a wireless link and uses spatial processing to improve link reliability (i.e., diversity gain) through diversity techniques or to provide higher data rates (i.e., multiplexing gain) through multiplexing schemes [1-2]. Diversity gain is a measure of enhanced robustness to signal attenuation, resulting in a higher signal-to-noise ratio (SNR) for 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 against a fixed error probability. The fundamental trade-offs between diversity and multiplexing in MIMO systems are described in [3-4].

[0064] 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 low SNR systems or channels characterized by low spatial selectivity. In contrast, spatial multiplexing can provide a significant data rate gain for channels with high SNR and high spatial selectivity. For example, Figure 1 shows that a cell can be divided into two regions: i) a multiplexing region 101 characterized by high SNR (attributed to proximity to cell towers or base stations), where spatial multiplexing can be used to increase the data rate by utilizing the spatial degrees of freedom of the channel; ii) a diversity region or cell edge 102, where spatial multiplexing is not as effective and diversity methods can be used to improve SNR and coverage (resulting only in a slight increase in data rate). Note that in Figure 1, the large circular area is marked with the shaded center of the circle as "Multifunctional Region" 101 and the area outside the shaded area of ​​the circle as "Diversity Region" 102. This same region name is used throughout Figures 1 to 4, where the shaded area is "Multifunctional Region" and the unshaded area is "Diversity Region", even if they are not labeled.

[0065] The LTE (version 8) and LTE upgrade (version 10) standards define a set of ten transport modes (TMs) [35, 85-86], which include a diversity or multiplexing scheme: ● Mode 1: Single antenna port, port 0 ● Mode 2: Transport Diversity ● Mode 3: Large Delay Cyclic Delay Diversity (CDD), used for the extension of open-loop spatial multiplexing in single-user MIMO (SU-MIMO). ● Mode 4: Closed-loop spatial multiplexing for SU-MIMO ● Mode 5: Multi-user MIMO (MU-MIMO) ● Mode 6: Closed-loop spatial multiplexing, using a single transport layer ● Mode 7: Single antenna port, UE-specific RS (port 5) ● Mode 8: Single or dual-layer transmission with UE-specific RS (port 7 and / or 8) ● Mode 9: Single 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)

[0066] We then describe diversity and multiplexing schemes commonly used in cellular systems and specific methods employed in LTE, as outlined above, and compare them with technologies specific to DIDO communications. We first identify two types of transmission methods: i) intra-cell methods (utilizing micro-diversity in cellular systems), which use multiple antennas to improve link stability or data rate within a cell; and ii) inter-cell methods (utilizing large-scale diversity), which allow for inter-cell cooperation to provide additional diversity or multiplexing gain. We then describe how our invention provides significant advantages over prior art (including spectrum capacity gain). [1.] [Internal Diversity Method] [ ]

[0067] Intracellular diversity methods operate within a single cell and are designed to increase SNR in cases of poor link quality (e.g., users at the cell edge suffer 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].

[0068] The diversity techniques supported by the LTE standard are transport diversity, closed-loop level 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, frequency switching transport diversity (FSTD) is implemented via space-frequency block code (SFBC) to take advantage of spatial and frequency selectivity

[31] . Level 1 precoding establishes a dedicated beam to a user based on quantization weights selected from a codebook (pre-designed using finite feedback techniques [36-42]) to reduce feedback surcharges from the user equipment (UE) to the base transceiver station (BTS 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] [ ]

[0069] MIMO multiplexing schemes [1, 19] provide data rate gains to support multiple parallel data streams on a wireless link in high SNR systems and in situations with sufficient spatial degrees of freedom within a channel (e.g., rich multipath environments with high spatial selectivity [16-18]).

[0070] 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. Depending on the UE request and the scheduler at the BTS, these weights can support two or four transmit antennas and one to four parallel data streams (identified by the number of layers in the precoding matrix). The LTE upgrade will include new transmission modes up to MIMO 8×8 to provide up to eight times the increase in spectral efficiency through spatial processing

[62] .

[0071] MU-MIMO schemes are defined for both UL and DL channels [31, 50]. In UL, each UE sends a reference signal to the BTS (consisting of a cyclic transfer version of the Zadoff-Chu sequence)

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

[0072] Intra-cell multiplexing techniques employing spatial processing only provide satisfactory performance in propagation scenarios characterized by high SNR (or SINR) and high spatial selectivity (rich multipath environment). For conventional large cells, these conditions are even more difficult to achieve because the BTS is usually far from the UE and the SINR distribution is usually centered at low values ​​

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

[0073] Other technologies and network solutions anticipated by LTE upgrades to 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 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. In this way, it can use the same RF chain for multiple channels and recombine multiple data streams in software. Intra-band CA requires different RF chains to operate at different portions of the spectrum and signal processing to recombine multiple data streams from different frequency bands.

[0074] The key concept of 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. Compared to the tall and expensive cell towers used for large cells, small cells are typically deployed through inexpensive access points with low-power transmission (as depicted in Figure 1). Two types of small cells are defined in LTE upgrades: i) metro cells, which are used for outdoor installations in urban areas and support 32 to 64 simultaneous users; and ii) microcells, which are used for indoor use and can serve up to 4 active users. One advantage of small cells is the higher UE density near the BTS, resulting in better SNR that can be increased through spatial multiplexing. However, many concerns remain regarding the practical deployment of small cells, especially regarding backhaul. Indeed, reaching individual small cells via high-speed wired connections to the BTS can be challenging, especially considering the high density of metro cells and microcells within a given coverage area. While line-of-sight (LOS) backhaul to small cells can often be implemented cheaply, there is generally no better practical LOS backhaul path available for small cell BTS placement compared to wired backhaul, and there is no general solution for non-line-of-sight (NLOS) radio backhaul to small cell BTSs. Finally, small cells require complex real-time coordination across BTSs to avoid interference such as in ad hoc networks (SON) [30, 51-52] and require complex cell planning tools (due to the higher density of small cells, even more complex than conventional cellular systems) to plan their optimal locations [48, 49].

[0075] Typically, there is no practical, general solution that allows small cells to coexist with large cells and achieve optimal, necessary, or even improved throughput. In numerous such unresolved situations, there are instances where the location of a small cell inevitably causes its UEs to overlap with the transmissions of a large cell, and both the small and large cells use the same frequencies to reach their respective UEs. In this situation, it is clear that the large cell transmission will interfere with the small cell transmission. While there may be methods to mitigate this interference for specific circumstances such as a particular large cell, a particular small cell, the specific large and small cell UEs involved, the throughput requirements of these UEs, 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 of a specific time interval. Generally, it is impossible to achieve full throughput to the channels of each UE. [3.] [Interval Partitioning Method] [ ]

[0076] Inter-cell transmission techniques enable cross-BTS cooperation to improve the performance of wireless networks. These techniques are a specific case of a method for achieving cross-transceiver cooperation in the general case of a distributed antenna network for multiple UEs simultaneously using the same frequency, as taught in related patents and applications [0002-0020]. Cross-BTS cooperation is described in

[53] to remove inter-cell interference for a specific case of a cellular system for a single UE at a given frequency at a given time. The system in

[53] divides large cells into multiple sub-cells and improves link robustness at a single UE at a single frequency (as it moves along the sub-cell boundaries) by employing dedicated beamforming from a coordinated BTS to improve the link robustness of a single UE at a single frequency.

[0077] More recently, this type of cooperative wireless cellular network has been defined in MIMO literature as "Network MIMO" or "Coordinated Multipoint" (CoMP) systems. Theoretical analysis and simulation results regarding the benefits gained from eliminating inter-cell interference in Network MIMO are presented in [54-61]. The key advantage of Network MIMO and CoMP is the removal of inter-cell interference in the overlapping areas 201 to 203 of the cells shown in Figure 2.

[0078] CoMP network actively became part of the LTE upgrade standard as a solution to mitigate inter-cell interference in next-generation cellular networks [62-64]. To date, the standard has proposed two CoMP solutions to remove inter-cell interference: i) Coordinated Scheduling / Beamforming (CS / CB), whereby the UE receives its data stream from only one BTS via beamforming and cross-BTS coordination to remove interference through beamforming or scheduling techniques; ii) Joint Processing (JP), where data about a given UE is jointly transmitted from multiple BTSs to improve the quality of the received signal and eliminate inter-cell interference. CoMP-JP achieves cross-BTS coordination at the cost of higher overhead in reload, resulting in a greater gain than CoMP-CS / CB. [4.] [Inter-area multiplexing method] [ ]

[0079] 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 of other users in the area. Given the increasing demand for aggregated bandwidth within a shared wireless spectrum and the growing need for reliable, predictable, and low-latency multi-user wireless networks for a given user, the limitations of prior art multi-user wireless technologies are evident. Indeed, prior art wireless technologies are insufficient to meet the increasing demand for reliable, predictable, and low-latency bandwidth due to the limited availability of spectrum suitable for certain types of wireless communication (e.g., wavelengths that effectively penetrate building walls).

[0080] Previous intracellular diversity and multiplexing techniques have provided up to a theoretical 4x increase in throughput for LTE (via MIMO 4x4) or at most a theoretical 8x increase for LTE upgrades (via MIMO 8x8), although higher orders of MIMO achieve improvements in reducing the increased throughput in a given multipath environment, especially as UEs (such as smartphones) become smaller and more constrained in terms of antenna placement. Further slight throughput gains in next-generation cellular systems can be achieved from additional spectrum allocations via carrier aggregation (e.g., the FCC National Broadband Program) and 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 for multi-user transmission because the spectral efficiency gains from spatial processing are limited.

[0081] While prior art inter-cell approaches (e.g., network MIMO and CoMP systems [53-64]) can improve the reliability of cellular networks by eliminating inter-cell interference, their capacity gains are only slight. In fact, these systems constrain the power transmitted from each BTS to confine it within the cell boundary, and the power leakage across cells only effectively eliminates inter-cell interference. Figure 2 shows an example of a cellular network with three BTSs 210-212 (each characterized by its own coverage area or cell). The power transmitted from each BTS 210-212 is constrained to limit the amount of inter-cell interference, depicted in Figure 2 by the areas where cells overlap. Because these systems operate within a low SINR framework in the interference region, their gain in spectral efficiency is only slight, similar to intra-cell schemes used for SU-MIMO. In order to achieve significant capacity gains in inter-cell cooperative networks, the power constraints at cell boundaries must be relaxed and spatial multiplexing should be enabled throughout cells with high SINR (instead of just at the cell edges with poor SINR performance as in previous techniques).

[0082] Therefore, it is expected to provide a system that achieves several orders of magnitude increase in spectral efficiency by removing any constraints on the power of transmissions via distributed BTSs and utilizing inter-cell multiplexing gains through spatial processing. Figure 3 illustrates a situation where the power of transmissions from three BTSs 301-303, all transmitting simultaneously at the same frequency, is increased, thereby allowing for interference at a higher level across the cell. In prior art systems, this interference would result in non-coherent interference (disrupting UE signal reception) in the interference region across the BTS. However, in embodiments of the present invention, this interference is utilized to establish a region of coherent interference (enhancing UE signal reception) around each UE through a novel inter-cell multiplexing method using spatial processing, thereby providing simultaneous, non-interfering data streams to each UE and increasing their inter-cell SINR.

[0083] In one exemplary embodiment of the invention, this inter-cell multiplexing gain is achieved through a distributed input distributed output (DIDO) system [0014-0020] and [77-78]. Figure 4 illustrates one example in which a number of additional access points 401 are added to intentionally increase the level of non-coherent interference across the cell, which is utilized in the invention to generate an area of ​​coherent interference around the UE and to generate inter-cell multiplexing gain. These additional BTSs may be low-power transceivers similar to inexpensive Wi-Fi access points, thereby providing a smaller area of ​​coverage overlap across a large cell, as shown in Figure 4.

[0084] We have observed that previous inter-cell methods, by deliberately limiting the transmission power from each BTS 210-212 as shown in Figure 2, ... [Avoiding out-of-homogeneity interference] and eliminating residual inter-cell interference (in overlapping areas between cells) through spatial processing, thereby providing an improved SINR and [Inter-BTS diversity gain]. In contrast, this invention achieves higher power transmission from each BTS. [Utilizing non-coherent interference] to establish coherent interference around the UE, thereby improving the system's ability to penetrate the cell through spatial processing. The necessary condition for [inter-cell multiplexing gain] is the signal quality at the UE. Therefore, the systems described in the prior art cannot be used to achieve inter-cell multiplexing gain via spatial processing because there is insufficient signal quality across the cell (due to the limited transmission power from the BTS) to achieve the inter-cell multiplexing method as described in this invention. Furthermore, the systems described in the prior art would be inoperable to achieve the multiplexing gain achieved in this invention, as depicted in Figures 3-4, given that prior art systems are designed to avoid inter-cell interference in the diversity area shown in the shaded areas of Figures 1-4, rather than utilizing inter-cell interference in the multiplexing area to obtain inter-cell multiplexing gain as achieved in this invention.

[0085] Embodiments of the present invention include a system and method for utilizing inter-cell multiplexing gain in a wireless communication network by employing a multi-antenna system (MAS) with multi-user (MU) transmissions (a multi-user multi-antenna system or "MU-MAS") via spatial processing. 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 only spatial processing methods are used to eliminate inter-cell interference. In another embodiment of the invention, the power transmitted from the multiple antennas is not constrained to any particular power level (as long as their equivalent power transmission levels are within regulatory or security limits), thereby intentionally establishing higher-level inter-cell interference across the cell that is utilized to achieve inter-cell multiplexing gain and increase the capacity of the wireless communication network.

[0086] In one embodiment, the wireless communication network is one of the cellular networks shown in Figures 1 and 2, such as a cellular network based on the LTE standard. In another embodiment of the invention, the wireless communication network is not constrained to any particular cell layout and the cell boundaries can extend to a larger area as shown in Figures 3 and 4. For example, the wireless communication network can be a wireless local area network (WLAN), a mesh network, an ad hoc network, a sensor network, a distributed antenna system, or a DIDO system with randomly placed access points without any transmission power constraints. However, these exemplary network structures should not be construed as limiting the general applicability of the invention to wireless communication networks. The invention can be applied to any wireless network in which multiplexing gain is achieved by transmitting signals from multiple antennas that interfere with reception at multiple UEs in order to establish simultaneous non-interference data streams to multiple UEs.

[0087] As illustrated in Figure 9, one embodiment of MU-MAS comprises a centralized processor 901, a base station network (BSN) 902, and M base transceiver stations (BTSs) 903 that wirelessly communicate with N user terminal devices, also known as user equipment (UEs) (illustrated as UEs 1-4). The centralized processor unit 901 receives N data streams via a network 900 (e.g., the Internet) containing different network content C1-5 (e.g., video, web pages, video games, text, voice, etc., streaming from a web server or other network resources) destined for different user terminal devices UEs 1-4. Hereinafter, we will use the term "data stream" to refer to any data stream transmitted via the network 900 that contains information that can be demodulated or decoded as an independent stream according to a specific modulation / coding scheme or protocol to generate any data including (but not limited to) audio, network, and video content. In one embodiment, the information stream can be transmitted as a sequence of bits of network content that has been demodulated or decoded from a separate stream.

[0088] Centralized processor 901 utilizes precoding transformations to combine (according to algorithms, such as those described in the relevant patents and applications) N information streams from network content into M bit streams. By way of example (but not limitation), precoding transformations can be linear (e.g., forced zeroing

[65] , block diagonalization [66-67], matrix inversion, etc.) or nonlinear (e.g., dirty paper coding [68-70] or Tomlinson halashima precoding [71-72], lattice techniques or lattice precoding [73-74], vector perturbation techniques [75-76]). Hereafter, we use the term "bit stream" to refer to any sequence of bits of network content that may not contain any useful bits of information and thus cannot be demodulated or decoded as a separate stream to extract the bits of the network content. In one embodiment of the present invention, the bit stream is a complex baseband signal generated by a centralized processor and quantized by a given number of bits to be sent to one of M transceivers.

[0089] In one embodiment, MAS is a distributed input distributed output (DIDO) system as described in relevant patents and patent applications. In this embodiment, the DIDO system comprises the following: ● [User device] [(UE) 1-4]: It is an RF transceiver used by fixed or mobile user terminals to receive data streams from DIDO backhaul via downlink (DL) channel and transmit data to DIDO backhaul via uplink (UL) channel. ● [Base mail and data collection] [tower] [(BTS) 903]: The BTS intersects DIDO reload and a radio channel. One embodiment of the BTS consists of a DAC / ADC and a radio frequency (RF) chain to convert baseband signals to an RF access point. In some cases, the BTS is a simple RF transceiver equipped with a power amplifier / antenna and carries RF signals to the BTS via RF-on-fiber technology as described in the relevant patents and applications. ● [Controller] [(CTR) 905]: A CTR 905 is a specific type of BTS designed for specific 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, and receiving channel status information (CSI) or channel quality information from the UE. One or more CTR stations can be included in any DIDO system. 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) technology 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; any other diversity techniques (such as antenna selection) can be employed to improve the radio link between the CTR and the UE. ● [Centralized Processor] [(CP) 901]: The CP is a DIDO server that intersects the Internet or other types of external networks with DIDO backhaul. In one embodiment, the CP calculates DIDO baseband processing and transmits waveforms to a distributed BTS for DL ​​transmission. ● [Base station network] [(BSN) 902]: A BSN is a network that connects a CP to a distributed BTS carrying information about DL or UL channels. A BSN is a wired or wireless network or a combination of both. For example, a BSN is a DSL, cable, fiber optic network, or line-of-sight (LOS) or non-line-of-sight (NLOS) wireless link. In addition, a BSN is a private network, a local area network, or the Internet.

[0090] We then describe how the DIDO system architecture described above can be incorporated into the LTE standard for cellular systems (and non-cellular systems utilizing the LTE protocol) to achieve additional gains in spectral efficiency. We begin with a general overview of the LTE architecture and modulation techniques used in DL and UL channels. Next, we provide a brief description of the physical layer frame structure and resource allocation in the LTE standard. Finally, we define DIDO precoding methods for downlink (DL) and uplink (UL) channels in multi-user scenarios using the LTE architecture. Regarding the DL scheme, we propose two solutions: open-loop and closed-loop DIDO schemes.

[0091] LTE is designed with a flat network architecture (as opposed to a layered architecture from previous cellular standards) to provide: reduced latency, reduced packet loss via ARQ, reduced call setup time, and improved coverage and throughput via large diversity. The network elements in the LTE network depicted in Figure 5 are

[79] : ● [GW] (Gateway) 501-502: This is a router that connects the LTE network to an external network (i.e., the Internet). GWs are divided into servo gateways that terminate the E-UTRAN interface ( [S-GW]) 502 and the PDN gateway that interfaces with the external network ( [P-GW]) 501. S-GW 502 and P-GW 501 are parts of the so-called Evolved Packet Core (EPC); ● [MME] (Motion Management Entity) 503: It manages mobility, security parameters, and UE identification codes. MME 503 is also part of the LTE EPC; ● [eNodeB] (Enhanced Node B) 504: It is a base station that handles radio resource management, user mobility, and scheduling; and ● [UE] (User Equipment) 505: Mobile station.

[0092] In one embodiment of the present invention, the LTE network is a DIDO network in which DIDO-UE is a UE in the LTE network, DIDO-BTS is an LTE eNodeB, DIDO-CTR is an LTE eNodeB or MME, and DIDO-CP is a DIDO network of an LTE GW.

[0093] An LTE frame has a duration of 10 milliseconds and consists of ten sub-frames as depicted in Figures 6a to 6c [33, 80]. Each sub-frame is divided into two time slots, each with a duration of 0.5 milliseconds. The LTE standard defines two types of frames: i) Type 1 for FDD operation, as shown in Figure 6a, where all sub-frames are assigned to either the downlink (DL) or uplink (UL) channel; ii) Type 2 for TDD operation, as shown in Figure 6b, where some sub-frames are assigned to the DL and some to the UL (depending on the selected configuration), while reserving some sub-frames for "special use". Each frame has at least one special sub-frame, which consists of three fields: i) a reserved downlink pilot time slot (DwPTS) for DL ​​transmission; ii) a guard period (GP); and iii) an uplink pilot time slot (UpPTS) for UL transmission.

[0094] LTE employs Orthogonal Frequency Division Multiplexing (OFDM), Orthogonal Frequency Division Multiple Access (OFMDA) modulation for DL, and Single Carrier FDMA (SC-FDMA) for UL. A "Resource Element" (RE) is the smallest modulation structure in LTE, consisting of one OFDM subcarrier in frequency and one OFDM symbol duration in time, as shown in Figure 7. A "Resource Block" (RB) consists of 12 subcarriers in frequency and one 0.5 millisecond time slot (depending on the type of DL channel and cyclic first code for UL, it consists of 3 to 7 OFDM symbol periods). [1. LTE] [Middle-downlink closed loop] [DIDO]

[0095] DIDO closed-loop schemes can be used in Time Division Duplex (TDD) or Frequency Division Duplex (FDD) systems. In FDD systems, the DL and UL channels operate at different frequencies, and therefore 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 and UL channels are set at the same frequency, and the system can employ closed-loop techniques utilizing channel reciprocity or open-loop schemes (as described in the following sections). The main advantage of closed-loop schemes is that they require feedback, resulting in greater additional information regarding control information via the UL.

[0096] One embodiment of the closed-loop scheme mechanism in the DIDO system is as follows: i) BTS 903 sends signaling information to UE via DL; ii) UE uses the signaling information to estimate DL Channel Status Information (CSI) from all "active BTSs"; iii) UE quantizes the DL CSI or uses a codebook to select precoding weights to be used for the next transmission; iv) UE sends the quantized CSI or codebook index to BTS 903 or CTR 905 via the UL channel; v) BTS 903 or CTR 905 reports the CSI information or codebook index to CP 901, which calculates the precoding weights for data transmission via DL. An "active BTS" is defined as the group of BTSs reached by a given UE. 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," both co-included in the application, we define a "user cluster" as a group of BTSs reached by a given UE. The number of active BTSs is limited to a user cluster to reduce the estimated CSI from the BTS to the given UE, thereby reducing the complexity of feedback add-ons on the UL and the DIDO precoding calculation at CP 901. [1.1] [LTE] [Standard downlink] [DIDO] [Send signal] [ ]

[0097] The LTE standard defines two types of reference signals (RS) that can be used 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 uncoded, while UE-specific RSs are precoded

[50] . CRSs are used in LTE Release 8, which employs codebook-based SU / MU-MIMO technology with up to four antennas in each cell. LTE Release 10 supports non-codebook-based SU / MU-MIMO schemes with up to eight transmit antennas and CoMP schemes with antennas distributed across different cells. Thus, Release 10 allows for more flexible signaling schemes via CSI-RS. In this invention, we describe how various types of signaling schemes can be used in DIDO systems to implement precoding. [1.1.1] [use] [CRS] [Of] [DIDO] [Send signal] [ ]

[0098] In the LTE (version 8) system, CRS is used to estimate the CSI from all transmit antennas at the BTS to the UE [80, 84]. CRS is obtained as a product of a two-dimensional orthogonal sequence and a two-dimensional pseudo-random number (PRN) sequence. There are three orthogonal and 170 possible PRN sequences, for a total of 510 different CRS sequences. Each sequence uniquely identifies a cell. CRS is transmitted in the first and last third OFDM symbols of each time slot and in each sixth subcarrier. For each transmit antenna at the BTS, an orthogonal pattern in time and frequency is designed for the UE to uniquely estimate the CSI from each of the four antennas. A high density of CRS with a 5% additional term in time and frequency is intentionally designed (i.e., transmitting in each 0.5 ms time slot and each sixth subcarrier) to support cases with fast channel changes with time and frequency

[83] .

[0099] In a real DIDO system, each UE may have more than four BTSs in its user cluster. For example, Figure 8 shows an SNR distribution for a real-world DIDO system deployment in downtown San Francisco, California. The propagation module is based on the 3GPP path loss / shading model

[81] and assumes a carrier frequency of 900 MHz. The dots in the figure indicate the location of the DIDO-BTS, and the black circles represent user clusters (with the UE located at the center of the circle). In sparsely populated areas, the UE may have only a few BTSs in its user cluster (e.g., as few as three BTSs in the example in Figure 8), while in densely populated areas, each user cluster may include up to 26 BTSs as shown in Figure 8.

[0100] The high redundancy of the CRS in a DIDO system can be used to achieve CSI estimation for any number of transmit antennas from four to more. For example, if the channel is fixed radio or characterized by low Doppler effect, it is not necessary to calculate the CSI from all four transmit antennas for 0.5 milliseconds (slot duration). Similarly, if the channel is frequency flat, the CSI estimation for each sixth subcarrier is redundant. In this case, resource elements (REs) occupied by the redundant CRS can be reallocated to other transmit antennas or BTSs in the DIDO system. In one embodiment of the invention, the system allocates resource elements of the redundant CRS to additional antennas or BTSs in the DIDO system. In another embodiment, the system estimates the time and frequency selectivity of the channel and dynamically allocates the CRS to different resource elements for different BTSs or only BTSs within a user cluster. [1.1.2] [use] [CSI-RS] [and] [DM-RS] [Of] [DIDO] [Send signal] [ ]

[0101] In the LTE Upgrade (Version 10) standard, each UE uses CSI-RS 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. As shown in Tables 6.10.5.2-1, 2 in

[33] , CSI-RS supports up to eight transmission antennas at the BTS. As shown in Table 6.10.5.3-1 in

[33] , CSI-RS is transmitted periodically within a range of 5 to 80 subcarriers (i.e., CSI-RS is transmitted every 5 to 80 milliseconds). The periodicity of CSI-RS in the LTE Upgrade is intentionally designed to be greater than that of CRS in LTE to avoid excessive additions to control information, especially for older LTE terminals that cannot utilize such additional resources. Another reference signal system used for CSI estimation is the demodulation-modulated RS (DM-RS). DM-RS is a demodulation reference signal sent to a specific UE and transmitted only in the resource block assigned to the UE.

[0102] When more than eight antennas (the maximum number of transmitters supported by the LTE Upgrade standard) are present in a user cluster, alternative techniques should be employed to implement DIDO precoding while maintaining system compliance with the LTE Upgrade standard. In one embodiment of the invention, each UE uses CSI-RS or DM-RS, or a combination of both, to estimate the CSI of 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 LTE Upgrade standard (supporting up to eight antennas). If not, the DIDO system employs alternative techniques to implement DL transmission from the BTS to the current UE. In one embodiment, the transmission power from the BTS is reduced until a maximum of eight BTSs are reachable by the UE within its user cluster. However, this solution may result in a reduction in data rate because coverage will be reduced.

[0103] Another solution is to divide the BTSs in the user cluster into several subsets and send a set of CSI-RS for each subset at a time. For example, if the CSI-RS period is 5 subframes (i.e., 5 milliseconds) as in Table 6.10.5.3-1 in

[33] , CSI-RS is sent from a new subset of BTSs for 5 milliseconds each. Note that this solution is feasible as long as the CSI-RS period is short enough to cover all BTS subsets within the UE’s channel coordination time (which is a function of the UE’s Doppler velocity). For example, if the selected CSI-RS period is 5 milliseconds and the channel coordination time is 100 milliseconds, then 20 BTS subsets of 8 BTSs each can be defined, totaling 160 BTSs in the user cluster. In another embodiment of the invention, the DIDO system estimates the UE’s channel coordination time and determines how many BTSs can be supported in the user cluster for a given CSI-RS period to avoid degradation attributable to channel changes and Doppler effects.

[0104] To date, proposed solutions for CSI-RS all adhere to the LTE standard and can be deployed within the architecture of conventional LTE systems. For example, the proposed method, which allows for more than eight antennas per user cluster, requires no modifications to the UE LTE hardware and software implementation, and only minor modifications to the protocols used for BTS and CP to enable selection of a subset of BTSs 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 systems. Alternatively, the constraints of the LTE standard can be relaxed, and slightly modified hardware and software for LTE UEs can be developed to support similar but non-LTE-compliant DIDO operating modes, allowing the UE to operate in either a fully LTE-compliant mode or a modified mode supporting non-LTE-compliant DIDO operation. For example, another solution is to increase the amount of CSI-RS to achieve a higher number of BTSs in the system. In another embodiment of the invention, different CSI-RS patterns and cycles are permitted as a method to increase the number of supported BTSs per user cluster. These minor modifications to the LTE standard are small enough that simple software changes can be made to use existing LTE UE chipsets. Alternatively, if hardware modifications are required for the chipset, the changes will be minor. [1.2 LTE] [Uplink within the standard] [DIDO CSI] [Feedback Method] [ ]

[0105] In the LTE and LTE upgrade standards, the UE feeds back information to the BTS to communicate its current channel conditions and the precoding weights for closed-loop transmission on the DL channel. These standards include three different channel indicators

[35] : ● Level indicator ( [RI]: This indicates how many spatial streams are transmitted to a given UE. This number is usually equal to or less than the number of transmission antennas. ● Precoding matrix indicator ( [PMI]: It is an index used for the codebook of precoding on DL channels. ● Channel quality indicator ( [CQI]: It defines the modulation and forward error correction (FEC) coding scheme to be used on DL to maintain a predefined error rate performance for a given channel condition.

[0106] Only one RI is reported for the entire bandwidth; however, depending on the frequency selectivity of the channel, PMI and CQI reports may be broadband or sub-band. These indicators are transmitted in the UL via two different types of physical channels: i) physical uplink control channel ( [PUCCH]), which is used only for control information; ii) Entity uplink shared channel ( [PUSCH] is used for both data and control information allocated on a resource block (RB) and on a subframe basis. On the PUSCH, the reporting procedures for RI, PMI, and CQI are periodic, and the indicators can be broadband (for frequency-flat channels) or UE-selected on a subband basis (for frequency-selective channels). On the PUSCH, the feedback procedure is aperiodic and can be UE-selected on a subband basis (for frequency-selective channels) or via a higher-level configured subband (e.g., for transmission mode 9 with eight transmitters in an LTE upgrade).

[0107] In one embodiment of the invention, the DIDO 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, if a larger number of indicators are required for DIDO precoding, the UE uses PUSCH to report additional indicators to the CP. If the channel is frequency-flat, the UE can utilize additional UL resources to report PMI for 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 if the channel is frequency-flat, the UE utilizes additional UL resources to report PMI for a larger number of BTSs. [2. LTE] [Downlink Open Loop] [DIDO]

[0108] The DIDO open-loop scheme can only be used in Time Division Duplex (TDD) systems that utilize channel reciprocity. One embodiment of the mechanism of the open-loop scheme in a DIDO system is as follows: i) UEs 1-4 transmit signaling information to BTS 903 or CTR 905 via UL; ii) BTS 903 or CTR 905 uses this signaling information to estimate the UL CSI from all UEs 1-4; iii) BTS 903 or CTR 905 performs RF calibration to convert the UL CSI to DL CSI; iv) BTS 903 or CTE 905 transmits the DL CSI or codebook index to CP via BSN 902; v) Based on the DL CSI, CP 901 calculates the precoding weights for data transmission via DL. Similar to the closed-loop DIDO scheme, user clustering can be used to reduce the amount of CSI estimated by the UE at the BTS, thereby reducing the computational burden at the BTS and the amount of signaling required at the UL. In one embodiment of the present invention, an open-loop precoding technique is used to transmit non-interference data streams from the BTS to the UE via the DL channel.

[0109] In LTE, there are two types of reference signals used for uplink channels [31, 33, 87]: i) Sounding Reference Signal (SRS), used for scheduling and link adaptation; ii) Demodulation Reference Signal (DMRS), used for data reception. In one embodiment of the invention, SRS or DMRS is used in an open-loop DIDO 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 (for a duration of 0.5 milliseconds) (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 that UE for UL data transmission.

[0110] 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, several DMRSs are generated from a basic Zadoff-Chu

[88] or computer-generated constant amplitude zero autocorrelation (CG-CAZAC) sequence by cyclic shifting of the base sequence. The base sequence is divided into 30 groups and adjacent 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., assuming a total signal bandwidth of 20 MHz), up to 110×30=3300 different sequences can be generated.

[0111] In one embodiment of the invention, the DIDO system assigns UEs to "virtual cells" to maximize the number of SRS or DMRS available in the UL. In an exemplary embodiment, the virtual cell is a coherence area around the UE (described in 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 coherence areas for different UEs. In another embodiment of the invention, each of 30 base sequences is assigned to a different DIDO cluster (defined in U.S. Patent No. 8,170,081, entitled "System And Method For Adjusting DIDO Interference Cancellation Based On Signal Strength Measurements," issued May 1, 2012) to reduce inter-cluster interference across adjacent DIDO clusters. In another embodiment, SRS or DMRS are assigned according to a specific frequency hopping pattern to utilize channel frequency diversity.

[0112] If there is insufficient orthogonal SRS or DMRS to simultaneously serve all UEs in the DL via DIDO precoding, an alternative is to multiplex the SRS or DMRS of different UEs in the time domain. For example, UEs are divided into different groups and SRS or DMRS for these groups is transmitted via consecutive time slots (each with a duration of 0.5 milliseconds). However, in this case, it is necessary to ensure that the period for allocating SRS or DMRS to different groups is lower than the channel co-location time of the fastest-moving UE. In fact, this is a necessary condition to ensure that the channel remains unchanged for all UEs from the time the CSI is estimated via SRS or DMRS to the time the system transmits the DL data stream to the UE via DIDO precoding. In one embodiment of the invention, the system divides active UEs into several groups and allocates the same group's SRS or DMRS to each group via consecutive time slots. In this same embodiment, the system estimates the shortest channel co-location time for all active UEs and calculates the maximum number of UE groups and the period for SRS or DMRS time multiplexing based on this information. [3.LTE] [Uplink in the middle] [DIDO] [technology] [ ]

[0113] Embodiments of the present invention employ an open-loop MU-MIMO scheme via UL channels to simultaneously receive UL data streams from all UEs to the BTS. One embodiment of the UL open-loop MU-MIMO scheme includes the following steps: i) UEs 1-4 transmit signaling information and data payloads to all BTSs 903; ii) BTS 903 uses the signaling information to calculate channel estimates from all UEs; iii) BTS 903 transmits the channel estimates and data payloads to CP 901; iv) CP 901 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 these UL channels in the frequency domain.

[0114] In one embodiment, synchronization between UEs is achieved via signaling from the DL and it is assumed that all BTS 903 are locked to the same time / frequency reference clock via direct wiring to the same clock or sharing a common time / frequency reference (in one embodiment via GPSDO). Variations in channel delay spread at different UEs can cause jitter between the time references of different UEs, which can affect the performance of the MU-MIMO method via UL. In one embodiment, the MU-MIMO method is used only for UEs within the same DIDO cluster (e.g., UEs that are close to each other) 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 1-4 at BTS 903.

[0115] The technique used to transmit signaling information regarding data demodulation on the UL can be the same method used for signaling in the downlink open-loop DIDO scheme described in the previous section. CP 901 can employ different spatial processing techniques to remove inter-channel interference from the UE data payload. In one embodiment of the invention, CP 901 employs nonlinear spatial processing methods such as maximum likelihood (ML), decision feedback equalization (DFE), or continuous interference cancellation (SIC) receivers. In another embodiment, CP 901 employs linear filters such as forced return-to-zero (ZF) or minimum mean square error (MMSE) receivers to cancel co-channel interference and demodulate the uplink data stream individually. [4.] [With existing] [LTE] [Network Integration] [ ]

[0116] In the United States and other parts of the world, LTE networks are already operational or under deployment and / or in the process of being deployed. It would be a significant benefit for LTE operators to gradually deploy DIDO capabilities to their existing or ongoing deployments. In this way, LTE operators can deploy DIDO in areas where they will receive the most direct benefits and gradually expand DIDO capabilities to cover more of their networks. When appropriate, once LTE operators have sufficient DIDO coverage in an area, they can choose to completely decommission cells and instead fully switch to DIDO, achieving higher spectrum density at a lower cost. Throughout this transition from cellular to DIDO, LTE operators' wireless customers will not see any loss of service. Instead, customers will only see improvements in their data throughput and reliability, while operators will see cost reductions.

[0117] Several embodiments exist that will gradually integrate DIDO into one of the existing LTE networks. In all cases, the BTS used for DIDO will be referred to as a DIDO-LTE BTS and will utilize one of the LTE-compatible DIDO embodiments described above or other LTE-compatible embodiments that may be developed in the future. Alternatively, the DIDO-LTE BTS will utilize a minor variant of one of the LTE standards described above and will update the UE (e.g., if a software update is sufficient to modify the UE to DIDO compatibility) or will deploy a new generation of DIDO-compatible UEs. In any case, the new BTS that will support DIDO within the constraints of the LTE standard or as a variant of one of the LTE standards will be referred to below as a DIDO-LTE BTS.

[0118] The LTE standard supports multiple channel bandwidths (e.g., 1.4, 3, 5, 10, 15, and 20 MHz). In one embodiment, an operator with an existing LTE network can allocate new bandwidth for LTE-DIDO BTS or redistribute existing LTE spectrum (e.g., redistribute 20 MHz into two 10 MHz blocks) to support a conventional LTE BTS in a cellular configuration in one block and a DIDO LTE BTS in another block. Effectively, this establishes two separate LTE networks, and UE devices will be configured to use one or the other network or select between the two. In the case of redistributed spectrum, the spectrum can be evenly divided between the conventional LTE network and the DIDO-LTE network, or more spectrum can be allocated to the network that best utilizes it, rather than evenly, based on the deployment level of cellular LTE BTS and DIDO-LTE BTS and / or UE usage patterns. This redistribution can be changed over time as needed, and at some point, when enough DIDO-LTE BTSs are deployed to provide the same or better coverage as cellular BTSs, all spectrum can be allocated to DIDO-LTE BTSs and cellular BTSs can be deactivated.

[0119] In another embodiment, conventional cellular LTE BTSs can be configured to coordinate with DIDO-LTE BTSs to share the same spectrum, but use it alternately. For example, if they share spectrum equally, each BTS network will alternately utilize a 10 ms frame time, e.g., a 10 ms frame for the cellular LTE BTS followed by a 10 ms frame for the DIDO-LTE BTS. Frame time can also be further divided at unequal intervals. This interval division can be changed as needed over time, and at a point when enough DIDO-LTE BTSs are deployed to provide the same or better coverage as the cellular BTSs, all time can be allocated to the DIDO-LTE BTSs and the cellular BTSs can be deactivated.

[0120] In another embodiment of the invention, DIDO is employed as a LOS or NLOS radio backhaul to small cells in LTE and LTE-upgraded networks. Since small cells are deployed in the LTE network, DIDO provides high-speed radio backhaul to these 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 more small cells cannot be added to a given area without causing inter-cell interference. In this same embodiment of the invention, DIDO BTS is used to gradually replace small cells, thereby utilizing inter-cell interference to provide increased network capacity. [refer to] [ ]

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[0209] 101: Multi-functional area 102: Diversity region / cell edge 201: Overlapping region 202: Overlapping region 203: Overlapping region 210: Base Transceiver Station (BTS) 211: Base Transceiver Station (BTS) 212: Base Transceiver Station (BTS) 301: Base Transceiver Station (BTS) 302: Base Transceiver Station (BTS) 303: Base Transceiver Station (BTS) 501: PDN Gateway (P-GW) 502: Servo Gateway (S-GW) 503: Management of Action Entity (MME) 504: Enhanced Node B (eNodeB) 505: User Equipment (UE) 900: Network 901: Centralized Processor (CP) / Centralized Processor Unit 902: Base Station Network (BSN) 903: Base Transceiver Station (BTS) 905: Controller (CTR)

Claims

1. A multi-antenna system (MAS) with multi-user (MU) transmission (“MU-MAS”), comprising: a plurality of antennas or wireless transceiver devices (BTS) (903) distributed over a coverage area, each wireless transceiver device having a cell ID. A plurality of wireless user equipment (UEs) communicatively coupled to the plurality of wireless transceiver devices (BTSs) and distributed throughout the coverage area; and a spatial processing unit (901) employing precoding to create a plurality of simultaneous non-interfering downlink (DL) data connections between the plurality of wireless transceiver devices (BTSs) (903) and the plurality of wireless user equipment (UEs) in the same frequency band by utilizing inter-channel interference between the plurality of wireless transceiver devices (BTSs) (903) and the plurality of wireless user equipment (UEs), or to create a plurality of simultaneous non-interfering uplink (UL) data connections between the plurality of wireless transceiver devices (BTSs) (903) and the plurality of wireless user equipment (UEs) in the same frequency band by utilizing inter-channel interference between the plurality of wireless user equipment (UEs); The plurality of wireless user equipment (UEs) maintain the plurality of simultaneous non-interference downlink (DL) data connections and the plurality of simultaneous non-interference uplink (UL) data connections throughout the entire coverage area of ​​one or more radio transceiver devices (BTSs).

2. The system of request item 1, wherein the multi-user (MU) transmission multi-antenna system (MAS) ("MU-MAS") is a mobile network (900).

3. The system as requested in item 2, wherein the mobile network (900) is compatible with the Release 8 3GPP protocol.

4. The system of request item 1, wherein the spatial processing unit (901) uses a closed-loop or open-loop precoding method to create the simultaneous non-interference downlink (DL) data links.

5. The system of request item 4, wherein a downlink (DL) or uplink (UL) reference signal is used to estimate the channel state information (CSI) of each of the plurality of user equipments (UEs).

6. In the system of request item 5, the uplink (UL) or downlink (DL) reciprocity is used to estimate the channel state information (CSI).

7. A method implemented in a multi-antenna system with multi-user transmission (MU-MAS), the method comprising: A plurality of radio transceiver devices (BTS) (903) are distributed over a coverage area, each BTS (903) having a cell ID; a plurality of user equipment (UE) are communicatively coupled to the plurality of radio transceiver devices (BTS); and precoding is employed to create a plurality of simultaneous non-interfering downlink (DL) data connections between the plurality of radio transceiver devices (BTS) (903) and the plurality of wireless user equipment (UE) in the same frequency band by utilizing inter-channel interference between the plurality of radio transceiver devices (BTS) (903), or to create a plurality of simultaneous non-interfering uplink (UL) data connections between the plurality of radio transceiver devices (BTS) (903) and the plurality of wireless user equipment (UE) in the same frequency band by utilizing inter-channel interference between the plurality of wireless user equipment (UE); The plurality of wireless user equipment (UEs) maintain the plurality of simultaneous non-interference downlink (DL) data connections and the plurality of simultaneous non-interference uplink (UL) data connections throughout the entire coverage area of ​​one or more radio transceiver devices (BTSs).

8. The method of claim 7, wherein the multi-user (MU) transmission multi-antenna system (MAS) ("MU-MAS") is a mobile network (900).

9. The method of request item 8, wherein the mobile network is compatible with the 3GPP version 8 protocol.

10. The method of claim 7, wherein the multi-user (MU) transmission multi-antenna system (MAS) ("MU-MAS") uses closed-loop or open-loop precoding to create the simultaneous non-interference downlink (DL) data links.

11. The method of claim 10, wherein the multi-user (MU) transmission multi-antenna system (MAS) ("MU-MAS") uses a downlink (DL) or uplink (UL) reference signal to estimate the channel state information (CSI) of each of the plurality of user equipments (UEs).

12. The method of claim 11, wherein the multi-user (MU) transmission multi-antenna system (MAS) ("MU-MAS") uses uplink (UL) or downlink (DL) reciprocity to estimate the channel state information (CSI).

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