Transmitter Space Shift Keying With Maximum- Ratio Combining and Receiver Spatial Modulation With Maximum-Ratio Transmission in Downlink Cellular Systems

<p>This thesis considers the analysis of matched filtering (MF) processing in massive multi-user multiple-input-multiple-output (MU-MIMO) wireless communication systems. The main focus is the analysis of system performance for combinations of two linear processers, analog maximum ratio combining (MRC) and digital MRC. We consider implementations of these processing techniques both at a single base-station (BS) and in distributed BS layouts. We further consider extremely low complexity distributed variants of MRC for such systems. Since MRC relies on the massive MIMO properties of favourable propagation (FP) and channel hardening, we also present a detailed analysis of FP and channel hardening. This analysis employs modern ray-based models rather than classical channel models as the models are more reliable for the large arrays and higher frequencies envisaged for future systems. The importance of MRC processing is being driven by the emergence of massive MIMO and millimetre wave as strong candidates for next generation wireless communication systems. Massive MIMO explores the spatial dimension by providing significant increases in data rate, link reliability and energy efficiency. However, with a large number of antennas co-located in a fixed physical space, correlation between the elements of antennas may have a negative impact. Distributed systems, where the total number of antennas are divided into different locations, make this problem less serious. Also, linear processing techniques, analog MRC and digital MRC, due to their simplicity and efficiency, are more practical in massive MU-MIMO systems. For these reasons we consider MRC processing in both co-located and distributed scenarios. Although distributed systems reduce the adverse impact of correlation caused by closely-spaced large antenna arrays by dividing the antennas into multiple antenna clusters, the correlation within the cluster still exists. Thus, we extend MRC analysis for massive MIMO to correlated channels. Approximations of expected per-user spectrum efficiency (SE) with correlation effects for massive MIMO systems with analog MRC and digital MRC are derived. Useful insights are given for future system deployments. A convergence analysis of the interference behaviour under different correlation models is presented. Furthermore, a distributed fully cooperative system, where all the received signals are sent to the central processor, offers attractive performance gains but at the cost of high computational complexity at the central node. Thus, we propose four low-complexity, two-stage processors, where only processed signals after local processing (first-stage) are transmitted to the global processing node (second-stage). We present analytical expressions for the expected per user SINR in an uplink distributed MU-MIMO system with two-stage beam-forming. This leads to an approximation of expected per-user SE. The analysis of both millimetre wave and massive MIMO systems requires a strong link to the physical environment and ray-based models are more practical and suitable for such systems. However, it is unclear how the key properties in conventional MIMO systems, such as FP and channel hardening, will behave in a ray-based channel model. In this thesis, remarkably simple and general results are obtained demonstrating that: a) channel hardening may or may nor occur depending on the nature of the channel models; b) FP is guaranteed for all models as long as the ray angles are continuous random variables; c) we also propose a novel system metric, denoted large system potential (LSP) as the ratio of the mean desired signal power to the total mean interference power, where both the numbers of antennas and end-users are growing to infinity at a fixed ratio. We derive simple approximations to LSP and demonstrate that LSP will not normally hold as the mean interference power usually grows logarithmically relative to the mean signal power.</p>

Multiple-input multiple-output (MIMO) has been accepted as a promising technology for its potential to achieve low bit error rate (BER) by space time coding [1] or to achieve large capacity by multiplexing [2]. MIMO multiplexing has been widely adopted to realize high speed data communications. The capacity of MIMO systems in the point-to-point transmission without external interferences has been studied in [3, 4] to show that large capacity can be achieved in a rich scattering environment. In a cellular environment, the same frequency/frequencies can be used in neighboring cells. As a result, co-channel interference exists and the channel between the base-station (BS) and the mobile-station (MS) is changed from noise-limited channel to interference-limited channel. Recently, the capacity of MIMO systems in the cellular environment has attracted much interest. Uplink (transmission from MS to BS) capacity with variable-rate transmissions is studied in [5]. By modeling the co-channel interference as additive white Gaussian noise (AWGN), the uplink capacity is also studied in [6, 7]. On the other hand, from the users’ stand point, the downlink capacity may be more interesting. However, the results for the downlink capacity of cellular MIMO systems presented in the literature are mainly based on the simulation results. Very detailed simulation results for the downlink MIMO capacity in 3G FDD WCDMA cellular systems can be found in [8]. By assuming single-frequency-reuse (the frequency reuse factor (FRF) equals to 1), the capacity of downlink cellular MIMO systems is studied by simulations and the results are presented in [9, 10]. These results are given in terms of the number of antennas, the modulation schemes, the propagation parameters as well as the cell size. However, FRFs other than 1 are not considered. By taking various FRFs into consideration, a comparative study on the capacity of cellular MIMO systems is presented in [11]. A comprehensive comparison between the capacity of SISO, SIMO, STBC-MISO and MIMO systems in a cellular environment is made based on the simulation results. In general, fixed FRF has been considered in cellular systems. It is reported in [12] that a flexible FRF may help to improve the capacity for cellular single antenna (SISO) systems. However, flexible design of FRF for cellular MIMO systems is rarely available in the literature. In this chapter, the downlink capacity of cellular MIMO systems is theoretically analyzed in terms of both the ergodic and outage capacities. The theoretical results of the best and worst situation capacities suggest that the greatest capacities may be achieved by using FRF 1 or FRF 3 adaptively according to the situations. Therefore, a hybrid frequency reuse scheme is

By using the time-varying channel responses of individual users, suitable dynamic resource allocation (DRA) strategies can improve resource utilization to provide broadband multimedia services of different QoS requirements over OFDM downlink in mobile cellular systems (Damji, N. and Le-Ngoc, T., ICC04, 2004). For non-realtime traffic, queueing can be used in conjunction with DRA to enhance further the system performance in terms of system spectral efficiency (b/s/Hz/cell) and system throughput. Performance of the proposed DRA schemes with queueing in various traffic and propagation conditions is evaluated and compared.

The effect of noise on the maximum useful number of receiver antennas that can be deployed in a cochannel interference diversity system is examined. The long term signal- power-to-interference-plus-noise-power ratio (SINRP), the long term signal amplitude to the square root of interference plus noise power ratio (SAINPR), the average instantaneous signal-to- interference-plus-noise ratio (AISINR), and the average bit error rate (BER) of a maximal ratio combining (MRC) diversity system in the presence of multiple cochannel interferers and additive white Gaussian noise (AWGN) are evaluated when the desired user signal and the interfering user signals are independent, and each of them experiences correlated Ricean fading at the receiver antennas. The results show that a previous design rule which states that the performance of a fixed-size antenna array containing the maximum number of independent antennas cannot be significantly improved by adding more than one additional antenna, still applies when the interference dominates the noise. It is shown that the SINRP and SAINPR measures exhibit asymptotic limits as the number of correlated antennas increases. Simple expressions for these limits are derived and it is shown that these asymptotic limits are unchanged when noise is neglected.

Outage capacity analysis of the massive MIMO diversity channel

In this paper, we study the performance of multiuser two-way relaying (TWR) system in cellular environment, wherein an N a -antenna base station (BS) wants to exchange information bidirectionally with one of the several single-antenna users (USs) with the aid of a fixed gain single-antenna relay terminal under different target rate requirements. In particular, we employ maximal ratio transmission (MRT)/maximal ratio combining (MRC) beamforming (BF) at the BS with user scheduling that maximizes the end-to-end signal-to-noise ratio (SNR). We deduce a new expression for the exact overall outage probability (OOP) of the considered system under independent and identically distributed (i.i.d.) Rayleigh fading channels. Moreover, we also derive a closed-form expression for the sum symbol error rate (SSER) to analyze the system error performance under various modulation schemes. Finally, the analytical findings are validated by the numerical and simulation results, and reveals that the diversity order of the considered system is independent of traffic asymmetry and decided by the minimum of the number of BS antennas and the number of USs.

This paper considers a downlink cellular system with decode-and-forward (DF) protocol. The multiple-antenna base station uses maximum-ratio transmission to communicate with the single-antenna mobile station (MS) through direct link and a DF relay station, and the MS utilizes maximum-ratio combining to deal with the received signal. Our interest herein lies in performance analysis for this practical cellular system. We derive exact expressions for the outage probability and the symbol error rate (SER) in closed-form. Moreover, a simple asymptotic approximation and a tight lower bound are presented for the outage probability and the SER respectively, based on which we propose two optimum power allocation schemes as well. Simulation results are provided to validate the theoretical analysis.

This paper investigates the achievable spectral efficiency (SE) of millimeter wave downlink cellular systems accounting for both small and large-scale fading effects. The base station (BS) employs a uniform linear array (ULA) and maximal ratio transmission. We derive the expectation of the squared inner product for different channel links under the assumption that the users are randomly distributed within a circular-shaped cell. Using this result, a new lower bound on the achievable SE, valid for arbitrary numbers of antennas is derived. The analytical results show that the achievable SE increases with the number of BS antennas, whilst it converges to a saturated value in the high signal-to-noise ratio (SNR) regime and larger inter- antenna spacing.

In the first part of the thesis we investigate bandwidth allocation in next generation cellular systems employing relays similar to LTE advanced systems with type-I relays. We jointly optimize the bandwidth and power usage under constraints on required rate, bandwidth and transmit power. We study scenarios wherein, the relay acts as a forwarder for multiple User Equipments (UEs/users) in both uplink and/or downlink. This includes scenarios when the relay has its own data to send along with forwarding the data of other users. We examine the weighted power minimization problem for relaying with multiple users. We also show specifi c results with N user scenario and also single user case in order to understand how the bandwidth and power are allocated. Numerical evaluations with N users on a three sector LTE-A cell employing Fractional Frequency Reuse (FFR) indicate that power savings of at least 3 dB can be achieved by optimizing over both bandwidth and power. Base stations with a large number of transmit antennas have the potential to serve a large number of users simultaneously at higher rates. They also promise a lower power consumption due to coherent combining at the receiver. However, the receiver processing in the uplink relies on the channel stimates which are known to su ffer from pilot contamination. In the second part of the thesis, we perform an uplink large system analysis of multi-cell multi-antenna system when the receiver employs a matched fi ltering and MMSE fi ltering with a pilot contaminated estimate. We find the asymptotic Signal to Interference plus Noise Ratio (SINR) as the number of antennas and number of users per base station grow large while maintaining a fixed ratio. To do this, we make use of the similarity of the uplink received signal in a multi-antenna system to the representation of the received signal in CDMA systems. The asymptotic SINR expression for both matched fi lter and the MMSE fi lter explicitly captures the e ffect of pilot contamination and that of interference averaging. This also explains the SINR performance of receiver processing schemes at di fferent regimes such as instances when the number of antennas are comparable to number of users as well as when antennas exceed greatly the number of users. Specifi cally, we explore the scenario where the number of users being served are comparable to the number of antennas at the base station. It is seen that MMSE fi lter is capable of suppressing the in-cell interference and that the interference power due to pilot contamination is the same as in a matched fi lter with a pilot contaminated estimate. We find the expression for the amount of interference suppression obtained using an MMSE filter which is an important factor when there are signi ficant number of users in the system as compared to the number of antennas. We validate the asymptotic expression through simulations and compare with an MMSE fi lter with a perfect estimate. Simulation results for achievable rate is close to theory for even a 10-antenna base station with 3 or more users per cell. In a typical set up, in terms of the five percentile SIR, the MMSE fi lter is shown to provide signifi cant gains over matched fi ltering and is within 5 dB of MMSE fi lter with perfect channel estimate. We also show that the achievable rates are within a 1 bit/symbol of the MMSE with perfect estimate when the number of users is comparable to the number of antennas.

This paper considers the uplink of a single-cell large-scale multiuser multiple-input multiple-output (MU-MIMO) system. The transmitted data is detected by linear receivers at the base station (BS), that is, maximum ratio combining (MRC), zero-forcing (ZF) and minimum mean square error (MMSE). New non-asymptotic outage expressions that are valid for any number of BS antennas are derived. It is shown that the MMSE scheme always achieves the best outage performance, and the ZF scheme outperforms the MRC scheme in the high signal-to-noise-ratio (SNR) regime, while the opposite holds in the low SNR regime. We also demonstrate that when the number of BS antennas is very large and the number of users is fixed, the asymptotic outage probability tends to zero, providing that the channel state information (CSI) is perfect. However, if both the number of BS antennas and the number of users grow large, it would be a different matter. Extensive numerical results are presented to verify the theoretical analysis.

On the maximal-ratio combining of FSO and RF links over generalized distributions and its applications in hybrid FSO/RF systems

This paper investigates a relay assisted simultaneous wireless information and power transfer (SWIPT) for downlink in cellular systems. Cooperative non-orthogonal multiple access (C-NOMA) is employed along with power splitting protocol to enable both energy harvesting (EH) and information processing (IP). A downlink model consists of a base station (BS) and two users is considered, in which the near user (NU) is selected as a relay to forward the received signal from the BS to the far user (FU). Maximum ratio combining is then employed at the FU to combine both the signals received from the BS and NU. Closed form expressions of outage propability, throughput, ergodic rate and energy efficiency (EE) are firstly derived for the SWIPT based C-NOMA considering both scenarios of with and without direct link between the BS and FU. The impacts of EH time, EH efficiency, power-splitting ratio, source data rate and distance between different nodes on the performance are then investigated. The simulation results show that the C-NOMA with direct link achieves an outperformed performance over C-NOMA without direct link. Moreover, the performance of C-NOMA with direct link is also higher than that for OMA. Specifically, (1) the outage probability for C-NOMA in both direct and relaying link cases is always lower than that for OMA. (2) the outage probability, throughput and ergodic rate vary according to beta, (3) the EE of both users can obtain in SNR range of from -10 to 5 dB and it decreases linearly as SNR increases. Numerical results are provided to verify the findings.

We analyze the performance of a dual-hop downlink cellular amplify-and-forward cooperative system in the presence of both channel estimation errors and radio frequency (RF) impairments, where multiple antennas are deployed only at the base station (BS) and single-antenna at relays and mobile stations (MS). Specifically, we derive approximate as well as exact closed-form expressions for the outage probability and expected spectral efficiency. In addition, simple asymptotic expressions at the high signal-to-noise ratio (SNR) regime are obtained, which facilitate the characterization of the achievable diversity order of the system. To validate the derived analytical expressions, we presented simulation results which are sufficiently tight across the entire range of SNRs. Findings of the paper suggest that full diversity order can be achieved only when the RF front-end hardware is assumed to be perfect, while in practice the imperfections in hardware are inevitable and reduce diversity order of the system. Moreover, the influence of key parameters such as the number of antennas, users, and relays on the system performance has been presented with the influence of the level of RF impairments.

We present a simulation study of two relaying schemes in downlink cellular systems. We simulate the performance of two relaying strategies: (i) a collaborative power addition (CPA) scheme, cooperative scheme where the relay collaborates with the base station, and (ii) a simple orthogonal relaying strategy where base stations and relays transmit in orthogonal time slots. Evaluations are done in the context of a 19-cell, 57-sector set-up in which each of the served users must be delivered a message. The user messages are taken to have the same size and 90% of users in the network must be served. All simultaneous transmissions mutually interfere. Improvements due to relay deployments are measured as throughput improvements in terms of increase in common rate of users as well as power savings in terms of reduction in peak or average power transmitted by base stations. We observe that the simpler orthogonal relaying scheme performs nearly as well as the more complex collaborative relaying in producing throughput gains and power savings.

In this work, a full‐duplex (FD) variable gain amplify‐and‐forward multi‐relay cooperative‐diversity system with(out) a direct path (DP) between the source and destination is studied over independent identically (non‐identically) distributed slow Rayleigh fading channels. Generalised relay selection, i.e. generalised selection transmission (GST) over relays is investigated for two extreme cases; single relay selection (RS) and use of all relays, i.e. maximum ratio transmission (MRT). By developing an equivalent link, the approximated probability density function (PDF) and cumulative distribution function (CDF) of a dual‐hop link with FD relay are obtained, thereafter, the adopted approximated PDF and CDF are offered. Then, approximated and asymptotic expressions for outage probability, moment generating function, and symbol error rate (SER) of GST with(out) DP are derived. Additionally, approximated ergodic capacity expressions are also obtained. All theoretical results validated by Manto Carlo simulation technique show that the proposed approximations of dual‐hop link with FD relay are robust and thus can be used to analyse such systems with FD relay, RS and MRT provide close performance which is significantly better than single relay. Additionally, for equal rates, substantial reduction in SER can be obtained by FD transmission as compared to half‐duplex one.