We consider fronthaul-limited generalized zero-forcing-based cell-free massive multiple-input multiple-output (CF-mMIMO) systems with multiple-antenna users and multiple-antenna access points (APs) relying on both cooperative beamforming (CB) and user-centric (UC) clustering. The proposed framework is very general and can be degenerated into different special cases, such as pure CB/pure UC clustering, or fully centralized CB/fully distributed beamforming. We comprehensively analyze the spectral efficiency (SE) performance of the system wherein the users use the minimum mean-squared error-based successive interference cancellation (MMSE-SIC) scheme to detect the desired signals. Specifically, we formulate an optimization problem for the user association and power control for maximizing the sum SE. The formulated problem is under per-AP transmit power and fronthaul constraints, and is based on only long-term channel state information (CSI). The challenging formulated problem is transformed into tractable form and a novel algorithm is proposed to solve it using minorization maximization (MM) technique. We analyze the trade-offs provided by the CF-mMIMO system with different number of CB clusters, hence highlighting the importance of the appropriate choice of CB design for different system setups. Numerical results show that for the centralized CB, the proposed power optimization provides nearly 59% improvement in the average sum SE over the heuristic approach, and 312% improvement, when the distributed beamforming is employed.

Massive multi-user multiple-input multiple-output (MU-MIMO) systems enable high spatial resolution, high spectral efficiency, and improved link reliability compared to traditional MIMO systems due to the large number of antenna elements deployed at the base station (BS). Nevertheless, conventional massive MU-MIMO BS transceiver designs rely on centralized linear precoding algorithms, which entail high interconnect data rates and a prohibitive complexity at the centralized baseband processing unit. In this paper, we consider an MU-MIMO system, where each user device is served with multiple independent data streams in the downlink. To address the aforementioned challenges, we propose a novel decentralized BS architecture, and develop a novel decentralized precoding algorithm based on eigen-zero-forcing (EZF). Our proposed approach relies on parallelizing the baseband processing tasks across multiple antenna clusters at the BS, while minimizing the interconnection requirements between the clusters, and is shown to closely approach the performance of centralized EZF.

The matrix-based differential encoding invoked by Differential Space-Time Modulation (DSTM) typically results in an infinite-cardinality of arbitrary signals, despite the fact that the transmit antennas (TAs) can only radiate a limited number of patterns. As a remedy, the recently developed differential spatial modulation (DSM) is capable of avoiding this problem by conceiving a beneficial sparse signal matrix design, which also facilitates low-complexity single-RF signal transmission. Inspired by this development, the differential space-time block code using index shift keying (DSTBC-ISK) further introduces a beneficial diversity gain without compromising the DSM's appealingly low transceiver complexity. However, the DSTBC-ISK's performance advantage tends to diminish as the throughput increases, especially when an increased number of Receive Antennas (RAs) is used. By contrast, the classic Differential Group Code (DGC) that actively maximizes its diversity gain for different multiple-input-multiple-output (MIMO) system setups is capable of achieving a superior performance, but its detection complexity grows exponentially with the throughput. Against this background, we propose the differential space-time shift keying using Diagonal Algebraic Space-Time scheme, which is the first DSTM that is capable of achieving the DGC's superior diversity gain at high throughputs without compromising the DSM's low transceiver complexity. As a further advance, we also conceive a new differential space-time shift keying using Threaded Algebraic Space-Time arrangement, which is capable of achieving an even further improved diversity gain at a substantially reduced signal detection complexity compared to the best DGCs. Furthermore, in order to strike a practical tradeoff, we develop a generic multi-element and multi-level-ring Amplitude Phase Shift Keying design, and we also arrange for multiple reduced-size DSTM sub-blocks to be transmitted in a permuted manner, which exhibits an improved diversity-throughput tradeoff.

Deploying intelligent transportation systems (ITS) is a promising solution to on-road safety, transportation efficiency and high data rate services for traveling vehicles. In ITS, vehicular networks (VN) are expected to be deployed together with traditional cellular networks (CN) to enhance the network access quality. As even for the same network, the quality of network access varies from location to location, mobile data offloading (MDO), which dynamically selects access network for vehicles, should be jointly considered with vehicle route planning to further improve the network access quality for individual vehicles and to enhance the performance of the entire ITS. In this paper, we investigate joint route and access network selection for an individual vehicle in a metropolitan scenario. We aim to improve the wireless data throughput of the target vehicle while guaranteeing its transportation efficiency requirements in terms of traveling time and distance. To achieve this objective, we first formulate the joint route and access network selection problem as a semi-Markov decision process (SMDP). The optimal policy of the SMDP is then derived based on value iteration. Sufficient simulations are conducted and numerical results demonstrate that the derived optimal policy significantly outperforms the existing work in terms of the total throughput and the late arrival ratio.

Today multiple radio access technologies (RATs) coexist in wireless networks. Multi-mode mobile terminals (MMTs) which can switch between networks with different RATs can enjoy enhanced quality of service (QoS) by exploring the diversity among different radio access networks (RANs). Usually, it has been assumed in literature that an MMT can access only one network at a time. Multi-Radio Access (MRA) is a technology that allows an MMT to transmit and receive data via multiple RANs simultaneously. With MRA, users can combine the data streams from multiple networks to meet their throughput requirements and enjoy customized QoS. In this paper, we consider an MMT with MRA technology in a heterogeneous network environment. It is assumed that the connection session of the MMT will spread over multiple handover windows and that the MMT is allowed to switch from the present set of connected RANs to another set at each handover window. We are interested in designing an intelligent network switching strategy which maximizes the average cumulative utility function of the MMT. Taking into account the dynamics of the heterogeneous networks, we model the network selection problem as a Markov decision process (MDP). By using the value iteration algorithm, we obtain the optimal switching strategy. Simulation results show that the MDP method provides higher average cumulative utility function and higher average rate of minimum throughput satisfaction than greedy method.

Millimeter-wave (mmWave) and sub-Terahertz (THz) communications are compelling as an enabler for next-generation wireless networks. In this paper, we study mmWave and sub-THz systems with array-of-subarray architecture. To accommodate the ultrabroad bandwidth in the mmWave and sub-THz bands, time-delay phase shifters are introduced in system design. Our goal is to investigate beamforming training with hybrid processing to extract the dominant channel information, which would fully exploit channel characteristics while respecting the nature of circuit hardware. In particular, codebooks based on time-delay phase shifters are defined and structured. Then, two multi-resolution time-delay codebooks are designed through subarray coordination. One is built on adaptation of physical beam directions, and the other relies on dynamic approximation of beam patterns. Also, a low-complexity system implementation with modifications on the time-delay codebooks is studied. Furthermore, based on the proposed codebooks, a hierarchical beamforming training strategy with reduced overhead is developed to enable simultaneous training for multiple users. Simulation results show that the proposed multi-resolution time-delay codebooks could provide sufficient beam gains and are robust over large bandwidth. Also, the effectiveness of the hierarchical beamforming training is verified.

For the sake of supporting massive connectivity in the future 5G networks, non-orthogonal multiple access (NOMA) techniques are advocated. As a promising NOMA technique, in recent years sparse code multiple access (SCMA) has attracted substantial attention. However, there is a paucity of studies on the theoretical analysis of its error-freely achievable data rate, especially, in the downlink context. Hence, we derive the cutoff rate of SCMA in downlink broadcast channels, which indicates the lower-bound of a system's error-freely achievable rate. However, we will demonstrate that when considering the conventional categorization of pairwise error events, the accuracy of the cutoff rate rapidly degrades in the low-SNR region owing to the fact that multi-user SCMA systems typically encounter an extremely large constellation size. Alternatively, by invoking Bergmans' concept from 1973 in the categorization of pairwise error events, we obtain a more accurate cutoff rate both in the low- SNR regions and the high-SNR regions. Moreover, we provide insights into the cutoff rate derivation process, which reveals some general guidelines for designing a beneficial codebook, capable of improving SCMA with respect to its original low-density signature-based counterpart.

Turbo detection performed by exchanging extrinsic information between the soft-decision QAM detector and the channel decoder is beneficial for the sake of exploring the bit dependency imposed both by modulation and by channel coding. However, when the soft-decision coherent QAM detectors are provided with imperfect channel estimates in rapidly fading channels, they tend to produce potentially unreliable LLRs that deviate from the true probabilities, which degrades the turbo detection performance. Against this background, in this paper, we propose a range of new soft-decision multiple-symbol differential sphere detection (MSDSD) and decision-feedback differential detection (DFDD) solutions for differential QAM (DQAM), which dispense with channel estimation in the face of rapidly fading channels. Our proposed design aims for solving the two inherent problems in soft-decision DQAM detection design, which have also been the most substantial obstacle in the way of offering a solution for turbo detected MSDSD aided differential MIMO schemes using QAM: 1) how to facilitate the soft-decision detection of the DQAM's amplitudes, which-in contrast to the DPSK phases-do not form a unitary matrix, and 2) how to separate and streamline the DQAM's soft-decision amplitude and phase detectors. Our simulation results demonstrate that our proposed MSDSD aided DQAM solution is capable of substantially outperforming its MSDSD aided DPSK counterpart in coded systems without imposing a higher complexity. Moreover, our proposed DFDD aided DQAM solution is shown to outperform the conventional solutions in literature. Our discussions on the important subject of coherent versus noncoherent schemes suggest that compared to coherent square QAM relying on realistic imperfect channel estimation, MSDSD aided DQAM may be deemed as a better candidate for turbo detection assisted coded systems operating at high Doppler frequencies.

A generalized adaptive network coding (GANC) scheme is conceived for a multi-user, multi-relay scenario, where the multiple users transmit independent information streams to a common destination with the aid of multiple relays. The proposed GANC scheme is developed from adaptive network coded cooperation (ANCC), which aims for a high flexibility in order to: 1) allow arbitrary channel coding schemes to serve as the cross-layer network coding regime; 2) provide any arbitrary trade-off between the throughput and reliability by adjusting the ratio of the source nodes and the cooperating relay nodes. Furthermore, we incorporate the proposed GANC scheme in a novel successive relaying aided network (SRAN) in order to recover the typical 50% half-duplex relaying-induced throughput loss. However, in support of the coherent detection, in addition to carrying out all the relaying functions, the relays have to estimate the Source-to-Relay channels, which imposes a substantial extra energy consumption and bit rate reduction owing to the inclusion of pilots. Hence noncoherent detection is employed for eliminating the power-hungry channel estimation. Finally, we intrinsically amalgamate our GANC scheme with the joint network-channel coding (JNCC) concept into a powerful three-stage concatenated architecture relying on iterative detection, which is specifically designed for the destination node (DN). The proposed scheme is also capable of adapting to rapidly time-varying network topologies, while relying on energy-efficient detection.

Conventional single-relay aided two-phase cooperative networks employing coherent detection algorithms incur a significant 50% throughput loss. Furthermore, it is unrealistic to expect that in addition to the task of relaying, the relay-station would dedicate further precious resources to the estimation of the source-relay channel in support of coherent detection. In order to circumvent these problems, we propose decode-and-forward (DF) based successive relaying employing noncoherent detection schemes. A crucial challenge in this context is that of suppressing the successive relaying induced interference, despite dispensing with any channel state information (CSI). We overcome this challenge by introducing a novel adaptive Newton algorithm based multiple-symbol differential interference suppression (MS-DIS) scheme. Correspondingly, a three-stage concatenated transceiver architecture is devised. We demonstrate that our proposed system is capable of near-error-free transmissions at low signal-to-noise ratios.

Differentially encoded and non-coherently detected transceivers exhibit a low complexity, since they dispense with complex channel estimation. Albeit this is achieved at the cost of requiring an increased transmit power, they are particularly beneficial, for example in cooperative communication scenarios, where the employment of channel estimation for all the mobile-to-mobile links may become unrealistic. In pursuit of high bandwidth efficiency, differential amplitude and phase shift keying (DAPSK) was devised using constellations of multiple concentric rings. In order to increase resilience against the typical high-Doppler-induced performance degradation of DAPSK and/or enhance the maximum achievable error-free transmission rate for DAPSK modulated systems, multiple-symbol differential detection (MSDD) may be invoked. However, the complexity of the maximum-a-posteriori (MAP) MSDD increases exponentially with the detection window size and hence may become excessive upon increasing the window size, especially in the context of iterative detection aided channel coded system. In order to circumvent this excessive complexity, we conceive a decomposed two-stage iterative amplitude and phase (A/P) detection framework, where the challenge of having a non-constant-modulus constellation is tackled with the aid of a specifically designed information exchange between the independent A/P detection stages, thus allowing the incorporation of reduced-complexity sphere detection (SD). Consequently, a near-MAP-MSDD performance can be achieved at a significantly reduced complexity, which may be five orders of magnitude lower than that imposed by the traditional MAP-MSDD in the 16-DAPSK scenario considered.

An amplify-and-forward (AF) based successive relaying aided network (SRAN) is designed for a multi-user spread-spectrum scenario conceived for noncoherent (NC) detection in order to convert the typical 50% half-duplex relaying-induced throughput loss to a potential user-load reduction of the CDMA system, where the NC detector allows us to avoid the extra power consumption imposed by channel estimation. With the same “green agenda” in mind, we limit the extra complexity imposed on the relay node (RN) by invoking the AF, rather than the more complex decode-and-forward protocol. We theoretically characterize the proposed AF based SRAN in the context of the DS-CDMA uplink by evaluating its noncoherent Discrete-input Continuous-output Memoryless Channel (DCMC) capacity. We demonstrate that the cooperative DS-CDMA uplink achieves a higher capacity gain with respect to its conventional direct transmission based counterpart, when the system has to support a high number of DS-CDMA users.

Conventional single-relay aided two-phase cooperative networks employing coherent detection algorithms incur a significant 50% throughput loss. Furthermore, it is unrealistic to expect that in addition to the task of relaying, the relay-station would dedicate further precious resources to the estimation of the source-to-relay channel in support of coherent detection, which would consume extra energy expended in power-hungry channel estimation. In order to circumvent these problems, we propose successive relaying employing noncoherent detection schemes. A crucial challenge in this context is that of suppressing the successive relaying induced interference, despite dispensing with any channel state information (CSI). We overcome this challenge by introducing a novel adaptive Newton algorithm based multiple-symbol differential interference suppression (MS-DIS) scheme. We demonstrate that our system is capable of near-error-free transmissions at low signal-to-noise ratios.

The conventional single-relay aided two-phase cooperative network employing a so-called soft-input soft-output multiple-symbol differential sphere detection (SISO-MSDSD) and operating in a distributed turbo decoding mode incurs a high complexity and imposes a 50% half-duplex relaying induced throughput loss. In this paper, we combat both of these critical problems. We commence by evaluating the Discrete-input Continuous-output Memoryless Channel (DCMC) capacity of the Decode-and-Forward (DF) based successive relaying aided networks (SRAN) as our theoretical benchmark. Then a relay-aided SISO-MSDSD is designed, which is then incorporated in the DF based SRAN. As our novel contribution, we demonstrate that the proposed transceiver is capable of significantly reducing the system's complexity, whilst recovering the 50% half-duplex relaying induced throughput loss. The system is capable of performing within 2.9 dB from the corresponding noncoherent DCMC capacity.

This paper presents a multiple-symbol differential spatial division multiple access (MS-DSDMA) system conceived for low-complexity and high-bandwidth-efficiency applications operating in time-varying fading channels, where no channel estimation is required. A low-complexity adaptive multiple-symbol differential interference suppression (MS-DIS) scheme is proposed, which is based on the maximum signal-to-interference-plus-noise ratio (MSINR) criterion and facilitates the implementation of the powerful multiple-symbol differential sphere detection (MSDSD). Then, a practical three-stage turbo DIS receiver design framework is proposed for the MS-DSDMA system, which is constituted by concatenating the adaptive DIS filter bank, the MSDSD and the channel decoder. Both the EXtrinsic Information Transfer (EXIT) chart analysis and the Monte-Carlo-based simulation results show that the proposed three-stage turbo DIS scheme is capable of achieving a substantially enhanced performance in comparison to the conventional linear minimum mean-squared error (LMMSE) based adaptive receiver. Furthermore, for the sake of significantly reducing the iterative detection complexity, two complexity reduction techniques are devised, namely the a priori-LLR-threshold (ALT) and the adaptive-window-duration (AWD) aided MSDSD schemes.

We propose Multiple-Symbol Differential Detection (MSDD) aided Differential Space-Time Block Codes (DSTBCs) using QAM. Our solution eliminates the requirement of high-complexity MIMO channel estimation and its pilot overhead, while mitigating the potential performance degradation of noncoherent receivers in fast fading channels. Additionally, we develop Multiple-Symbol Differential Sphere Detection (MSDSD) for the QAM aided DSTBC schemes advocated, in order to circumvent their potentially excessive complexity.

It is widely recognized that half-duplex-relay-aided differential decode-and-forward (DDF) cooperative transmission schemes are capable of achieving a cooperative diversity gain, while circumventing the potentially excessive-complexity and yet inaccurate channel estimation, especially in mobile environments. However, when a cooperative wireless communication system is designed to approach the maximum achievable spectral efficiency by taking the cooperation-induced multiplexing loss into account, it is not obvious whether or not the relay-aided system becomes superior to its direct-transmission based counterpart, especially, when advanced channel coding techniques are employed. Furthermore, the optimization of the transmit-interval durations required by the source and relay is an open issue, which has not been well understood in the context of half-duplex relaying schemes. Hence, we first find the optimum transmission duration, which is proportional to the adaptive channel-code rate of the source and relay in the context of Code-Rate-Optimized (CRO) TDMA-based DDF-aided half-duplex systems for the sake of maximizing the achievable network throughput. Then, we investigate the benefits of introducing cooperative mechanisms into wireless networks, which may be approached in the context of the proposed CRO cooperative system both from a pure capacity perspective and from the practical perspective of approaching the Discrete-input Continuous-output Memoryless Channel (DCMC) capacity with the aid of the proposed Irregular Distributed Differential (IrDD) coding aided scheme. In order to achieve a near-capacity performance at a low-complexity, an adaptive-window-duration based Multiple-Symbol Differential Sphere Detection (MSDSD) scheme is employed in the iterative detection aided receiver. Specifically, upon using the proposed near-capacity system design, the IrDD coding scheme devised becomes capable of performing within about 1.8 dB from the corresponding single-relay-aided DDF cooperative system's DCMC capacity.

It is widely recognized that differential decode-and-forward (DDF) cooperative transmission scheme is capable of providing a superior performance compared to classic direct transmissions employing differential detection, where no channel coding is used. However, the diversity gains achieved by the cooperative system become modest in practical channel coded scenarios, where the interleaving and channel coding gains dominate. Therefore, when a cooperative wireless communication system is designed to approach the maximum achievable spectral efficiency by taking the cooperation-induced multiplexing loss into account, it is not obvious, whether or not the relay-aided system becomes superior to its direct-transmission based counterpart, especially, when advanced channel coding techniques are employed. Hence in this paper the capacity of the single-relay-assisted DDF based cooperative system was studied in comparison to that of its direct-transmission based counterpart in order to answer the above-mentioned dilemma.

This paper presents an Irregular Distributed Hybrid Concatenated Differential (Ir-DHCD) coding scheme contrived for the relay-aided differential decode-and-forward (DDF) cooperative system using multiple-symbol differential sphere detection (MSDSD), where no channel estimation is required. We proposed a practical design framework for a cooperative system, which is capable of performing close to the network's corresponding non-coherent Discrete-input Continuous-output Memoryless Channel (DCMC) capacity. An adaptive-window-duration based MSDSD scheme is employed to further reduce the iterative detection complexity. Specifically, upon using the proposed near-capacity system design, the Ir-DHCD coding scheme devised becomes capable of performing within about 1.8 dB from the corresponding single-relay-aided DDF cooperative system's DCMC capacity.

In multi-user cellular uplinks cooperating mobiles may share their antennas in order to achieve transmit diversity by formig a virtual antenna array (VAA) in a distributed fashion. In this paper, based on the minimum BER criterion, we investigate cooperating-user-selection (CUS) and adaptive-power-allocation (APA) for two types of differentially modulated cooperative cellular uplinks requiring no channel state information (CSI) at the receiver, namely, for the differential-amplify-and-forward (DAF) and the selective differential-decode-and-forward (DDF) assisted systems. More specifically, we investigate the cooperative-protocol-selection (CPS) of the uplink system in conjunction with a beneficial CUS as well as the APA scheme in order to further improve the achievable end-to-end performance, leading to a resource-optimized hybrid cooperative system. Hence, a number of cooperating MSs may be adaptively selected from the available MS candidate pool and the cooperative protocol employed by a specific cooperating MS may also be adaptively selected in the interest of achieving the best possible BER performance.

It is widely recognized that the differential amplify-and-forward (DAF) transmission scheme is capable of providing a superior performance compared to classic direct transmissions employing differential detection in slow-fading channels and in fact it may even outperform coherent detection aided systems relying on realistic imperfect channel estimates. However, in reality the channels connecting the multiple nodes of a cooperative system typically become time-selective due to the relative mobility of the cooperating terminals. Hence, the performance gain achieved may erode as the environment becomes more time-selective. On the other hand, multiple-symbol based differential sphere detection (MSDSD) has been proposed to mitigate the channel-induced performance loss suffered by classic direct transmission schemes employing the conventional differential detection (CDD) scheme. Hence in this paper, we specifically design the MSDSD based on a multidimensional tree search, which is capable of achieving a significant performance gain in the context of a DAF-aided cooperative system for transmission over time-selective channels. For example, given a target BER of 10 3, a performance gain of about 10 dB can be attained by the proposed MSDSD for a two-user cooperative system in a channel having a normalized Doppler frequency of 0.03.

Recently, the turbo-detected sphere packing (SP) aided space-time block-coding (STBC) STBC-SP scheme was demonstrated to provide useful performance improvements over conventionally-modulated orthogonal design-based STBC schemes in the context of single-user multiple-input multiple-output (SU-MIMO) systems. Hence, in this letter, we extend its employment to the multiuser MIMO (MU-MIMO) scenario. For the sake of achieving a near maximum a posteriori (MAP) performance while imposing a moderate complexity, we specifically design theK-best sphere detection (SD) scheme for supporting the operation of the SP-modulated system, since the conventional SD cannot be directly applied to such a system. Consequently, with the aid of our modified SD, a significant performance gain can be achieved by the SP-modulated system over its conventionally-modulated counterpart in the context of MU-MIMO systems.

It is widely recognized that the differential amplify-and-forward (DAF) transmission scheme is capable of providing a superior performance compared to classic direct transmissions employing differential detection in slow-fading channels and in fact it may even outperform coherent detection aided systems relying on realistic imperfect channel estimates. However, in reality the channels connecting the multiple nodes of a cooperative system typically become time-selective due to the relative mobility of the cooperating terminals. Hence, the performance gain achieved may erode as the environment becomes more time-selective. Hence in this paper, we specifically design the multiple-symbol based differential sphere detection (MSDSD) for the DAF-aided cooperative system, which is capable of achieving a significant performance gain for transmission over time-selective channels.

In multiuser cellular uplinks, cooperating mobiles may share their antennas in order to achieve transmit diversity by formig a virtual antenna array (VAA) in a distributed fashion. In this paper, based on the minimum BER criterion, we investigate cooperating-user-selection (CUS) and adaptive-power-allocation (APA) for two types of differentially modulated cooperative cellular uplinks requiring no channel state information (CSI) at the receiver, namely, for the differential-amplify-and-forward (DAF) and the selective differential-decode-and-forward (DDF) assisted systems. They both employ multiple-symbol differential sphere detection (MSDSD) to combat rapid-fading-induced performance degradation. More specifically, we investigate the cooperative-protocol-selection (CPS) of the uplink system in conjunction with a beneficial CUS as well as the APA scheme in order to further improve the achievable end-to-end performance, leading to a resource-optimized hybrid AF/DF cooperative system.

Recently, the turbo-detected sphere packing (SP) aided space-time block-coding (STBC) STBC-SP scheme was demonstrated to provide useful performance improvements over conventionally-modulated orthogonal design based STBC schemes in the context of single-user multiple-input multiple-output (SU-MIMO) systems. Hence, in this treatise we extend its employment to the multi-user MIMO (MU-MIMO) scenario. For the sake of achieving a near maximum a posteriori (MAP) performance while imposing a moderate complexity, we specifically design the K-best sphere detection (SD) scheme for supporting the operation of the SP-modulated system, since the conventional SD cannot be directly applied to such a system. Consequently, with the aid of our modified SD, a significant performance gain can be achieved by the SP-modulated system over its conventionally-modulated counterpart in the context of MU-MIMO systems. For example, a performance gain of 3.5 dB can be achieved by the proposed 256-SP over the identical-throughput 16-QAM benchmark system in the scenario of a four-receive-antenna SDMA uplink (UL) system supporting two users both employing Alamouti's G2space-time code, given a target BER of 10-4.

Based on an Extrinsic Information Transfer (EXIT) chart-assisted receiver design, a low-complexity near-Maximum A Posteriori (MAP) detector is constructed for high-throughput systems. A high throughput is achieved by invoking high-order modulation schemes or multiple transmit antennas, while employing a novel sphere detector (SD) termed as a center-shifting SD scheme. The center-shifting SD is assisted by the MMSE soft- interference-cancellation (SIC-MMSE) algorithm. The resultant scheme is capable of attaining a considerable complexity reduction over the conventional SD-aided iterative benchmark receiver. For example, the SIC-MMSE center-shifting scheme may enable the iterative receiver to achieve a near-MAP performance in the challenging scenario of an (8 x 4)-element rank-deficient 4-QAM SDM/OFDM system. This near-MAP performance is achieved, despite imposing a reduced detection-candidate-list-generation- related complexity, which is about an order of magnitude lower than that exhibited by the list-SD dispensing with the proposed center-shifting scheme. As a further benefit, the computational complexity associated with the extrinsic LLR calculation was reduced by a factor of about 64. The associated memory requirements were also reduced by a factor of 64.

Based on an extrinsic information transfer (EXIT) chart assisted receiver design, a low-complexity near-maximum a posteriori (MAP) detector is constructed for high-throughput MIMO systems. A high throughput is achieved by invoking high-order modulation schemes and/or multiple transmit antennas, while employing a novel sphere detector (SD) termed as a center-shifting SD scheme, which updates the SD's search center during its consecutive iterations with the aid of channel decoder. Two low-complexity iterative center-shifting SD aided receiver architectures are investigated, namely the direct-hard-decision center-shifting (DHDC) and the direct-soft-decision center-shifting (DSDC) schemes. Both of them are capable of attaining a considerable memory and complexity reduction over the conventional SD-aided iterative benchmark receiver. For example, the DSDC scheme reduces the candidate-list-generation-related and extrinsic-LLR-calculation related complexity by a factor of 3.5 and 16, respectively. As a further benefit, the associated memory requirements were also reduced by a factor of 16.

When the maximum number of best candidates retained at each tree search level of the K-Best Sphere Detection (SD) is kept low for the sake of maintaining a low memory requirement and computational complexity, the SD may result in a considerable performance degradation in comparison to the full-search based Maximum Likelihood (ML) detector. In order to circumvent this problem, in this contribution we propose a novel complexity-reduction scheme, referred to as the Apriori-LLR- Threshold (ALT) based technique for the A'-best SD, which was based on the exploitation of the a priori LLRs provided by the outer channel decoder in the context of iterative detection aided channel coded systems. For example, given a BER of 10-5, a near- ML performance is achieved in an (8 times 4)-element rank-deficient 4-QAM system, despite imposing a factor two reduced detection candidate list generation related complexity and a factor eight reduced extrinsic LLR calculation related complexity, when compared to the conventional SD-aided iterative benchmark receiver. The associated memory requirements were also reduced by a factor of eight.

Iterative if-best sphere detection (SD) and channel decoding is appealing, since it is capable of achieving a near- maximum-a-posteriori (MAP) performance at a low complexity. However, a potentially excessive computational cost is imposed, especially in a high-throughput Spatial Division Multiplexing (SDM) aided OFDM system employing a large number of transmit antennas and/or high-order modulation schemes. This problem is further aggravated, when the number of transmit antennas exceeds that of the receive antennas, namely in the challenging scenario of rank-deficient systems. In order to further reduce the complexity imposed, we propose a unity-rate-code-aided (URC) three-stage concatenated transceiver constituted by an inner and outer channel encoder/decoder pair as well as the SDM aided OFDM transmitter and K-best SD. We have demonstrated that our proposed three-stage scheme is capable of achieving a substantial performance gain over the classic two-stage scheme. For example, given a target Bit Error Ratio (BER) of 10 5, the three-stage SD-aided receiver is capable of achieving a performance gain of 4 dB over its two-stage counterpart in an (8 x 4)-element SDM/OFDM system. Furthermore, we have also investigated the achievable performance of our novel center- shifting aided SD in the context of this three-stage scheme. Consequently, an additional 0.5 dB performance gain can be attained. Finally, the convergence behavior of the proposed schemes were studied with the aid of 3D Extrinsic Information Transfer (EXIT) charts and their 2D projections.