In this paper, we propose a novel downlink multiple access system with a multi-antenna transmitter and two single-antenna receivers, inspired by the underlying principles of hierarchical quadrature amplitude modulation (H-QAM) based multiple access (QAMA) and space-division multiple access (SDMA). In the proposed scheme, coded bits from two users are split and assigned to one shared symbol and two private symbols carried by different beams. Based on joint symbol mapping of H-QAM constellations and phase-aligned precoding at the transmitter, each receiver observes a different H-QAM constellation with Gray mapping, a unique parallax feature not shared by existing schemes. In addition to avoiding successive interference cancellation (SIC), each user independently demodulates its own bits on separate I and Q branches with calculations based on closed-form expressions. Hence the receiver complexity is on par with that of orthogonal multiple access (OMA), which is much lower than that in other competing alternatives such as non-orthogonal multiple access (NOMA) and rate-splitting multiple access (RSMA). We carry out system optimization and determine the achievable rate region. Numerical results show that the proposed system achieves superior performance compared with benchmark schemes employing SIC-free receivers, and further demonstrates competitive results across various performance metrics even relative to benchmark schemes relying on SIC-based receivers. The proposed scheme is attractive to 6G and IoT applications where the increased system complexity is at the transmitter while the receivers maintain low complexity.

In this paper, we propose a nonorthogonal downlink multiple access scheme, where the base station assigns the bit streams to different users from an adjustable hierarchical quadrature-amplitude-modulation (QAM) constellation and all users deploy a simple non-iterative receiver with the same complexity as in an orthogonal multiple access (OMA) system. We analyze the achievable information rates of the proposed scheme, termed as QAMA, and show that it possesses a similar rate region as the hybrid OMA and MUST approach in the 5G standard, while the latter relies on successive interference cancellation (SIC) receivers and dynamic switching of two distinct modules. We propose a design procedure to determine a few transmission modes that closely approximate the rate region via a simple polygon. Thanks to the receiver simplicity, easy scalability to more than two users, and the near-optimal rate region, QAMA is an appealing candidate for 6G cellular and other advanced wireless systems.

Abstract The evolution of the fifth-generation (5G) new radio (NR) has progressed swiftly since the third generation partnership project (3GPP) standardized the first NR version (Release 15) in mid-2018. Nowadays, the world’s leading carriers are competing to provide various commercial services over 5G networks. Looking ahead to 2025 and beyond, it is expected that over 6.5 million 5G base stations will be installed to offer services to over 58% of the world’s population via over 100 billion 5G connections. Following the rapid development of 5G, an increasing number of commercialization use cases will drive the 5G network to continuously improve performance and expand capabilities. Hence, it is the right time to consider a well-defined framework and standardization for 5G NR evolution (5G-Advanced) to support commercialization between 2025 and 2030. First, this study addresses the key driving forces, requirements, usage scenarios, and capabilities of 5G-Advanced; then, it highlights the main technological challenges and introduces the top 10 promising technological directions in detail. Finally, other fascinating technological directions in 5G-Advanced are shortly mentioned.

We propose a novel radio-frequency (RF) receiving architecture based on the microelectromechanical system (MEMS) and optical coherent detection module. The architecture converts the received electrical signal into mechanical vibration through the piezoelectric effect and adopts an optical detection module to detect the mechanical vibration. We analyze the response function of the piezoelectric film to an RF signal, the noise-limited sensitivity of the optical detection module, and the system transfer function in the frequency domain. A simple on–off keying (OOK) modulation with carrier frequency 1 GHz is used to numerically evaluate the detection sensitivity. The result shows that considering the main noise sources in system, the signal detection sensitivity can reach around −116.6 dBm at bandwidth 5 MHz. Such sensitivity significantly outperforms that of the currently deployed long-term evolution (LTE) system. Finally, we conduct preliminary experiments based on an off-the-shelf aluminium nitride piezoelectric film, which shows that the vibration amplitude based on the theoretical prediction can be achieved.

Resonant beam communications (RBCom) is capable of providing wide bandwidth when using light as the carrier. Besides, the RBCom system possesses the characteristics of mobility, high signal-to-noise ratio (SNR), and multiplexing. Nevertheless, the channel of the RBCom system is distinct from other light communication technologies due to the echo interference issue. In this article, we reveal the mechanism of the echo interference and propose the method to eliminate the interference. Moreover, we present an exemplary design based on frequency shifting and optical filtering, along with its mathematic model and performance analysis. The numerical evaluation shows that the channel capacity is greater than 15 b/s/Hz.

We adopt artificial$\Lambda $-type three-level system with superconducting devices for microwave signal detection, where the signal intensity reaches the level of discrete photons instead of continuous waveform. Based on the state transition principles of the three-level system, we propose a statistical model for microwave signal detection. In addition, achievable transmission rates and signal detection based on the proposed statistical models are investigated for low temperature conditions in deep space communication scenario. It is predicted that high sensitivity can be achieved by the proposed system. We further characterize the received signal considering the saturation phenomenon of three-level system, which reveals negligible performance degradation caused by saturation under weak received power regime.

WiFi fingerprinting-based indoor localization system is extensively researched with the advent of the high-density wireless networks deployment, but is limited by heavy site survey in the offline phase, for which fingerprint augment is an effective solution. In this paper, we innovatively propose a fingerprint augment method based on super-resolution (FASR) and formulate the processing framework. In order to perform super-resolution on sparse fingerprint database, the conversions between WiFi fingerprint data and fingerprint images are proposed. EDSR, a method based on deep learning in super-resolution, is adopted in FASR to obtain high-resolution fingerprint images, which are then reconstructed to augmented fingerprint database. Experiments on simulated and real scenarios verified the feasibility of FASR. Our work demonstrates a new application of machine learning in wireless communication.

Federated learning(FL) enables massive distributed Information and Communication Technology (ICT) devices to learn a global consensus model without any participants revealing their own data to the central server. However, the practicality, communication expense and non-independent and identical distribution (Non-IID) data challenges in FL still need to be concerned. In this work, we propose the Semi-Federated Learning (Semi-FL) which differs from the FL in two aspects, local clients clustering and in-cluster training. A sequential training manner is designed for our in-cluster training in this paper which enables the neighboring clients to share their learning models. The proposed Semi-FL can be easily applied to future mobile communication networks and require less uplink transmission bandwidth. Numerical experiments validate the feasibility, learning performance and the robustness to Non-IID data of the proposed Semi-FL. The Semi-FL extends the existing potentials of FL.

Voice traffic prediction is significant for network deployment optimization thus to improve the network efficiency. The real entropy based theorectical bound and corresponding prediction models have demonstrated their success in mobility prediction. In this paper, the real entropy based predictability analysis and prediction models are introduced into voice traffic prediction. For this adoption, the traffic quantification methods is proposed and discussed. Based on the real world voice traffic data, the prediction accuracy of N-order Markov models, diffusion based model and MF model are presented, among which, 25-order Markov models performs best and approach close to the maximum predictability. This work demonstrates that, the real entropy can also predict voice traffic well which broaden the understanding on the real entropy based prediction theory.

We propose content compression coding for massive users, where correlated contents of grouped users can be utilized to achieve high compression efficiency. We divide the users into several groups. For each group, we select the group head, encode the information of group head independently, and encode other users referring to the group head. We formulate the grouping optimization problem, transform it to a zero-one discrete optimization problem as well as a subset selection problem, and provide upper and lower bounds on the compression ratio. We investigate the sufficient condition and necessary condition on the optimality of one user group. We also investigate two specific type of sources, with star-type and chain-type user statistics, and provide the optimal user grouping. The compression ratio is also studied from both theoretical and experimental perspectives.

Multiple access technology is facing a great challenge posed by the upcoming massive Machine-Type Communication (mMTC). Traditional grant-based random access (RA) schemes are not competent to tackle the massive connectivity and small infrequent data packets of mMTC, because of the intolerable signalling overhead and delay. Grant-free random access joint with non-orthogonal multiple access (NOMA) may be suitable for the mMTC services as it reduces the signaling overhead. However, user collisions are still possible and damage the system's performances. In this paper, we propose a grouping-based grant-free random access based on statistical user rate information in which the base station (BS) divides MTDs into several groups according to the users' rate distribution and allocates proper radio resources for each group. BS broadcasts this grouping determinations to all MTDs with a small amount of signaling and MTD then randomly selects a group to access the channel on their own instant data rates. We analyze the blocking rate and provide an optimization method for deciding the grouping policy. Simulations prove the proposed scheme outperforms the traditional non-grouping RA even if there are some estimation errors.

We address the matching-based communication system optimization over parallel channels in wide spectrum. The dimension of the logarithm channel link gain vector can be reduced significantly under certain line-of-sight millimeter wave and optical wireless communication scenarios. We design the quantization points in the reduced dimensional space and store the optimal scheduling policy corresponding to each quantization point. We first investigate the covariance of the achievable rates of the parallel channels and the system outage probability. Then, we formulate a system optimization framework via matching the link gains of parallel channels to the quantization points, and obtain the sufficient conditions such that the utility loss of employing the quantization-based solution can be sufficiently small under sufficiently small quantization distortion in the reduced dimensional space. Such sufficient conditions can be satisfied for certain common optimization examples. We also address the matching-based communication system design under noisy channel estimation via providing a probabilistic upper bound on the utility loss in terms of the quantization design and channel estimation pilot. It can be shown that with sufficiently large probability the utility loss due to the quantization can be sufficiently small, if the quantization distortion is sufficiently small and the pilot energy is sufficiently large.

Future fifth generation (5G) wireless networks will be challenged by the huge amount of mobile data traffic, especially from enormous Machine Type Communication(MTC) devices, so in this paper we proposed Aggregation Coding Multiple Access(ACMA) for MTC downlink transmissions, which exploits the inherent correlation among aggregated users in spatial domain to improve the spectrum efficiency. By assuming the data traffic together with the delay requirements of MTC devices can be perfectly predicted based on wireless big data analysis, the transmission order of multicast downlink data traffic from base stations to multiple terminals could be adjusted by proposed aggregation coding technique using much less timeslots. We then evaluated the performance of conditional random search(CRS), standard-row algorithm(SRA) and Genetic Algorithm(GA) to optimize the data traffic transmission order compared to Multimedia Broadcast Multicast Service (MBMS) and simulation results validated the performance of ACMA and the optimization of GA. Our work shed light on dealing with massive MTC data traffic for future wireless communications.

The frequency reuse technique is a fundamental and classical issue in the interference management of cellular networks, and has never experienced any fundamental shifts from the first generation to the current LTE. With the development of 5G, the classic frequency reuse (FR) is no longer suitable for heterogeneous cellular networks (HCNs). In this paper, we propose a unified frequency reuse (UFR) model for a heterogeneous networking architecture in future wireless cellular communications, where the HCN is divided into different tiers with different frequency band assigned. Then, we take an HCN with different overlapped tiers of densely deployed base stations as an example and analyze the spectral efficiency, transmission ability and energy efficiency of the network when the proposed UFR scheme is applied. The numerical results demonstrate that the proposed model is not only beneficial to the frequency allocation but also achieves higher performance for future 5G wireless communications.

In this paper, we consider the delay tolerable data traffic transmission in Heterogeneous Networks (HetNet) and propose a flow-level-delay constraint small cell sleeping scheme to achieve energy saving gain. We use the flow-level model to capture the process of data transmission in micro base station (BS) which is the small cell we consider. Our scheme takes advantage of the feature of HetNet and designs macro BS cooperation in the process of dynamic micro BS sleeping, which helps achieve more energy saving. Through the Markov state transfer diagram and solving the balance equation, we get the numeric performance of power consumption and delay in our scheme. Then we solve a cost function minimization problem to get the optimal energy-delay tradeoff curve which helps to get the sleep scheme parameter settings. Our work cast light on how the energy consumption and delay performance is affected by dynamic sleep control and HetNet environment. And finally simulation shows that our proposed scheme can achieve better energy saving.

In this paper, we propose a novel Over Frequency Ruse (OFR) scheme in a heterogeneous network structure for 5G to increase the cell spectral efficiency and transmission ability. Specifically, we first derive an explicit expression of the interference characteristic in the cellular networks based on the cell interference depth (CID) model. And then, we analyze the performance of the proposed OFR including the cell spectral efficiency, the area throughput and the energy efficiency, and compare them with those of the traditional FFR cellular networks. The results demonstrate that the proposed OFR scheme improves the performance effectively, no matter the spectral efficiency or the energy efficiency, and is compatible with the traditional FR and FFR in 3G and 4G.

Though cooperative relaying is believed to be a promising technology to improve the energy efficiency of cellular networks, the relays' static power consumption might worsen the energy efficiency therefore can not be neglected. In this paper, we focus on whether and how the energy efficiency of cellular networks can be improved via relays. Based on the spatial Poisson point process, an analytical model is proposed to evaluate the energy efficiency of relay-assisted cellular networks. With the aid of the technical tools of stochastic geometry, we derive the distributions of signal-to-interference-plus-noise ratios (SINRs) and mean achievable rates of both non-cooperative users and cooperative users. The energy efficiency measured by “bps/Hz/W” is expressed subsequently. These established expressions are amenable to numerical evaluation and corroborated by simulation results.

Energy efficiency in cellular networks has recently received a significant attention and incorporating cooperative relays in cellular networks is believed to be a promising technology to greatly lower the energy consumption of cellular networks while sustaining high data rates. In this paper, we focus on improving energy efficiency of a single cellular system assisted by relays. We propose a novel relay deployment strategy and a corresponding relay selection procedure. Using coded cooperation as the transmission scheme, we derive the area power consumption under a target area spectral efficiency. Besides, the impact of different parameters such as cell radius, target area spectral efficiency, number and position of relays on the area power consumption is also studied. Compared with direct transmission and decode-and- forward (DF) relaying, our work significantly improves the energy efficiency of cellular systems and sheds key insights into the tradeoff between the energy consumption and the spectral efficiency via dynamically adjusting the resource allocation between BS and relay in coded cooperation.

In cellular networks, base station must reserve some resource for the possible handoff which affects the energy efficiency of the system. In this paper, we establish a theoretical model to maximizing the energy efficiency (EE) from the aspects of users' mobility and service duration. After analyzing the probability of handoff in service with user mobility and service characteristics, we introduce a dynamic energy efficiency (DEE) function. With the DEE function, an optimization problem under the constraint of maximal power is formulated to determine the optimal cell radius to maximize the DEE. We prove the existence of the unique optimal cell radius and propose an algorithm to solve the problem. Numerical results show the relationship between the optimal cell radius and different users' mobility and service characteristics, and indicate that the optimal radius is increasing both in the users' average velocity and in the average service duration. This work can provide a reliable theoretical basis for green design of cellular networks.

In this paper, we propose a new definition of energy efficiency with respect to a given target packet error rate (PER). It is shown that some previous reported definitions are actually special cases of our definition. Consequently we use the definition to analyze the energy efficiency of Multilevel quadrature amplitude modulation (MQAM) and find that for a specific transmission there exists an energy efficient optimal initial PER which is independent of the traffic QoS. Then we derive the optimal PER and corresponding transmission power, and analyze the properties under various channel gain conditions. We believe that the result may help improve the energy efficiency of adaptive modulation. Finally, we consider the delay constraints and propose an optimization method based on PER to achieve extra energy efficiency gain while satisfying the delay requirements.

Adaptive modulation is one of key technologies in wireless communication systems. The modulation order can be adaptively adjusted via different space-time coding under constrained transmission rate. Constellation-constrained capacity of different modulations under the constrained transmission rate and the adaptive modulation and space-time coding(AM-STC) scheme are analyzed in this paper. Analysis suggests that lower modulation satisfying the transmission rate can get higher spectrum efficiency at high SNRs and the simulations show that the AM-STC scheme is helpful to select the best modulation at low SNRs. Moreover, the simulation results are reasonable agreement with the results of theoretical analysis.

This paper proposes a new power control algorithm in multicell networks. It improves the capacity of the cellular network significantly by balancing the utilization of the radio resource and the resulting co-channel interference. In particular, we employ a leader-followers game model to jointly consider the benefits of the users and the network. A global price policy is adopted to optimize the capacity of the whole network by eliminating the users with bad channel conditions. We prove that this game converges to a unique optimal equilibrium in a largescale interference-ideal network. And a price update function is presented to adjust the price adaptively. Simulation results show that this algorithm holds 33-50% capacity gains over the noncooperative game strategy, and achieves comparable performance with the high-complexity centralized geometric programming method even in small-scale networks.

Spectrum sensing is a key technology in cognitive radio (CR) and cooperative spectrum sensing is derived due to the effects of channel fading. In this paper, we focus on the optimal number of secondary users in cooperative spectrum sensing to maximize the utility in CR network. By considering both the detection error probability and the resource used by the secondary users in cooperation, we derive the analytical suboptimal number of secondary users in a special CR network where all the SUs have the same SNR. The simulation results show that the utility of suboptimal scheme is greater than that of other schemes and nearly the same as that of the optimal scheme with exhaust search.

Coded Cooperation (CC) is a promising user cooperation scheme. In this paper, we propose a novel network- coding-based coded cooperation scheme. When a user decodes its partner's information correctly in the first frame, it transmits the combination of the partner's parity bits and its own parity bits through network coding in the second frame. This is distinct from the classical scheme, where the user only transmits the partner's parity bits during cooperation. We analyze the outage probability of the proposed scheme, and show that it achieves a full diversity order. Numerical evaluations reveal that the proposed scheme outperforms the classical scheme when the inter-user channels are poor. Also, the results show that the proposed scheme always outperforms no cooperation in various channel conditions while the performance of classical scheme is worse than that of no cooperation with the poor inter-user channels. This means that the performance of the proposed scheme is stabler than the classical scheme and the proposed scheme is more tolerant to the poor inter-user channels.

Using group theory, we analyze cycle GF(2p) codes that use Cayley graphs as their associated graphs. First, we show that through row and column permutations the parity check matrix H can be put in a concatenation form of row-permuted block-diagonal matrices. Encoding utilizing this form can be performed in linear time and in parallel. Second, we derive a rule to determine the nonzero entries of H and present determinate and semi-determinate codes. Our simulations show that the determinate and semi-determinate codes have better performance than codes with randomly generated nonzero entries for GF(16) and GF(64), and have similar performance for GF(256). The constructed determinate and semi-determinate codes over GF(64) and GF(256) can outperform the binary irregular counterparts of the same block lengths. One distinct advantage for determinate and semi-determinate codes is that they greatly reduce the storage cost of H for decoding. The results in this correspondence are appealing for the implementation of efficient encoders and decoders for this class of promising LDPC codes, especially when the block length is large.

In this paper, we propose a new double parameters controlled cross-layer adaptive resource allocation scheme for heterogeneous types of traffic in multiuser OFDM system. Unlike the existing resource allocation scheme, the proposed double parameters controlled scheme don't focus on the design of packet utility function (PUF), but by controlling values of two parameters: "delay compensatory factor" and "throughput compensatory factor" respectively, to achieve diverse levels of tradeoff between traffic QoS satisfaction and system power efficiency flexibly. The existing PUFs may be applied in the proposed scheme, where double parameters controlled scheduling is followed by subcarrier-power allocation, considering not only queue state, random packet arrival and delay in the MAC layer but also transmit power limit and time varying wireless channel in the PHY layer. In addition, PUFs tailored for a specific type of traffic may be suit to systems with other types of traffic as well as with heterogeneous types of traffic. Fairness among different types of traffic can be guaranteed as well. Simulations confirm the flexibility and efficiency by the proposed scheme.

In this paper, we propose a new fairness criterion based on QoS satisfaction of users. Unlike the existing throughput fairness criterion suitable for non-realtime traffic and the existing delay fairness criterion tailored for real-time traffic, the proposed QoS satisfaction criterion handles heterogeneous traffics in an unified fashion. Based on the new fairness criterion, we propose a cross-layer resource allocation scheme for downlink multiuser OFDM with heterogeneous traffics, where user scheduling is followed by subcarrier-bit allocation. The resource allocation depends on not only the channel state information (CSI) and QoS requirements of users, but also random packet arrivals and queue states. Simulations confirm significant performance improvement and user QoS satisfaction fairness by the proposed scheme.

This paper presents a new cross-layer resource allocation model for multiuser OFDM systems, where the packet arrival process, delay QoS in the application layer and the subcarrier conditions for all users in the physical layer are considered in the MAC layer design. The objective of the proposed cross-layer resource allocation is formulated into a constrained optimization problem, which incorporates the three layers into an integrated framework. To solve the problem effectively, we propose a complexity-reduced elitist selection genetic algorithm (ESGA). Numerical examples demonstrate the effectiveness of our proposed algorithm. Due to its low computational complexity, our proposed algorithm is very suitable for implementation in a practical system.

This paper presents an improved norm-based user selection algorithm for multiuser MIMO systems with block diagonalization. Our motivation is to reduce the complexity of the original norm-based algorithm while keeping the throughput performance. The main ideas consist of applying a heuristic Gram-Schmidt orthogonalization in the design of precoding matrix and constructing a user-reduced set that is semiorthogonal to the already selected users in each iteration. Numerical examples demonstrate the effectiveness of our proposed algorithm. The low computational complexity makes it very suitable for implementation in a practical system.

In an effort to utilize the advantage of using multiple antennas, transmit antenna selection for linear dispersion codes (LDC-TAS) is proposed in this paper. We present three criteria: maximum channel gain, maximum capacity and max-min post-SNR, for selecting the optimal transmit antennas when linear, coherent receiver is used over a slowly varying channel. Simulation results suggest that the max-min post-SNR criterion outperforms the other selection methods in a variety of modulation modes, such as QPSK, 8PSK and 16QAM. Compared with BLAST-TAS, under the same spectral efficiency, LDC-TAS shows significant diversity advantage. In low SNR environment, LDC-TAS is still better than STBC-TAS

A blind method for joint estimation of the frequency offset and the channel in an OFDM system is presented in this paper. Estimation is achieved in three successive steps. First, the channel containing the frequency-offset component is estimated by means of subspace techniques. The result is then used in the second step, which is cyclostationarity-based, to obtain the frequency offset. Third, the channel can be achieved by removing the frequency-offset component from the result of the first step. Finally, based on the above three steps, an iterative method is used to get more accurate estimation of the channel and the frequency offset. Mathematical deduction and simulation results are both shown that the proposed method is effective, and is superior to methods introduced in two earlier papers.

A velocity-adaptive channel estimation method using a lowpass filter is proposed. The bandwidth of the filter is determined by searching the spectrum autocorrelation results for the second highest peak location. The components which are higher than the maximum Doppler frequency are forced to zeros because they are just from noise if there is no spectrum leakage, which is in fact not the real case due to the truncation in the time domain. Therefore, a compensation for the removed leaking signal is made after zero forcing (ZF). Computer simulation shows that, in a wide range of mobile speed, the performance of the proposed estimation method in terms of the mean square error (MSE), is close to that of the ideal case in which Doppler frequency is perfectly known, and the compensation for the leaking signals improves the accuracy of channel estimation.

In the distributed antenna systems (DAS), if it is assumed that there is no power cooperation among the distributed antenna modules, namely, with the per-antenna constraints, the antenna module can cover less area than that with the total power constraints only. In this paper, a triangle cellular communication system (TCCS) and its power control scheme are proposed. Then, we investigate the information-theoretic capacity of TCCS based on the single-user assumption and multi-cell environment. Through simulation, we find that TCCS has a smooth capacity distribution in deferent parts of the cell. The numerical results show that TCCS can enlarge its covering area with the per-antenna constraints. Furthermore, TCCS with its power control scheme gets a capacity as about 2 times high as that with the traditional power control scheme.

V-BLAST(Vertical Bell Lab Layered Space-time) is an attracting space-time code structure because it can get significantly higher capacity than SISO system in Rayleigh fading environments. To optimize ber, computational complexity, time delay or other targets, many different detection algorithms are proposed in recent years. In this paper, we proposed a two-stage detection algorithm for V-BLAST, in the first stage, conventional algorithm such as ZF, MMSE is used; in the second stage, based on the detection result of the front stage, we adopt an iterative successive symbol cancellation algorithm to obtain better ber performance at a little cost. The effect of iterations and different cancellation order are also analyzed in our paper. Furthermore, we adopt partial successive symbol cancellation in our structure to avoid error propagation.

A new scheme, selective time domain filtering, that has significantly reduced complexity compared to the SLM scheme, which only relies on conventional channel estimation and demodulation techniques for multipath fading channels to recover the data, is proposed. Computer simulations indicate that the new scheme suffers only a small loss in performance in exchange for significant reduction in complexity.

A low complexity per-antenna power control (PAPC) approach based on minimum mean squared error (MMSE) detector for V-BLAST is proposed in this paper. The PAPC approach is for minimum bit error rate (BER) averaged over all substreams, when the data throughput and the total transmit power keeps constant over time. Simulation results show that the power-controlled V-BLAST (P-BLAST) outperforms the conventional V-BLAST is terms of BER performance with MMSE detector, especially in presence of spatial correlation between antennas. When MMSE detector is adopted, the P-BLAST can achieve comparable BER performance to that of conventional V-BLAST with maximum likelihood (ML) detector

A closed-form expression for the pairwise error probability of cyclic unitary space-time codes with t=2 and r=1 is obtained. Additionally, this result is used to obtain an upper bound to the symbol error rate of cyclic unitary differential space-time group codes. It is also shown that these techniques can be used to approximate the symbol error rate of dicyclic unitary differential space-time group codes.

Abstract Digital beamforming (DBF) techniques are capable of improving the performance of communications systems significantly. However, if the transmitted signals are conflicted with strong interference especially in the direction of the transmitted beams, these directional jamming signals will severely degrade the system performance. In order to efficiently mitigate the interference of the directional jammers, in this contribution a beam‐hopping (BH) communications scheme is studied. In the BH communications scheme, only one pair of the beams is used for transmission and it hops from one to the next according to an assigned BH pattern. In this contribution, a range of expressions in terms of the average signal to interference plus noise ratio (SINR) performance have been derived, when both the uplink and downlink are considered. The average SINR performance of the BH scheme and that of the conventional single‐beam (SB) as well as multiple‐beam (MB) assisted beam‐processing schemes have been investigated. Our analysis and results show that the BH scheme is capable of efficiently combating the directional jamming, with the aid of utilizing the directional gain of the beams generated by both the transmitter and the receiver. Furthermore, the BH scheme is capable of reducing the intercept probability of the communications. Therefore, the BH scheme is suitable for communications when several distributed antenna arrays are available around a mobile. Copyright © 2005 John Wiley & Sons, Ltd.

We develop a novel scheme to track carrier frequency offset in time domain differential modulation and demodulation OFDM systems. Compared with existing methods, this scheme is more bandwidth efficient and easier to implement. Simulation results in the Rayleigh fading channel show that this frequency tracking scheme can work robustly under relatively low SNR conditions.

By applying the rate-distortion theory to multiple-input-multiple-output (MIMO) systems, we first present the mathematical relation between feedback rate and closed-loop capacity. The lower and upper bounds on rate are then presented. Finally, we perform simulations of the bounds for various SNRs and numbers of antennas, and draw relevant conclusions. The proposed concepts and expressions of the bounds, the conclusions and numerical results, as well as the method that employs the rate-distortion theory to study feedback of MIMO systems, are crucial to researches and designs based on a global consideration of SNR, antenna number, feedback rate and capacity.

Future wireless communications systems are required to efficiently utilize the limited wireless spectrum resource due to the rapidly growing demands for services, packetized transmission over wireless link makes it possible to achieve a high statistical multiplexing gain. Previous MAC protocols pay more attention to maximizing system performance with guaranteed quality of service (QoS). This article presents a channel-hold- based reservation (CHBR) MAC protocol that deals with the tradeoff between system performance and system overhead. The performance evaluation is conducted by simulation with different parameters.

Digital beamforming (DBF) techniques improve the performance of communications systems significantly. However, if the communications are strongly jammed in the direction of the transmitted beam, the directional jamming will severely degrade the performance of the systems. In order to solve this problem, the paper proposes a beam hopping (BH) communications scheme. The analysis results of the average SINK performance show that compared with the conventional single beam (SB) and multibeam (MB) communications scheme, the new BH communications scheme is capable of combating the directional jamming efficiently, while fully utilizes the directional gain of the beams of the transmitters and the receivers. Moreover, the BH scheme can reduce the intercept probability of the communications to some degree. Therefore, the BH scheme is a promising communications scheme with a good performance-cost trade-off.

OFDM (orthogonal frequency division modulation) is a very promising technique for future communication system. However, frequency offset is well known as one of the main factors that influence the performance of OFDM communication systems. Various coarse frequency synchronization algorithms based on differential detection have been proposed to cope with the oscillation in frequency response in dispersive channel. This paper extends the concept of differential detection and improves existing coarse frequency offset synchronization algorithm. In this modified algorithm, parameter can be adjusted to obtain different performance tradeoff. In addition, compared with the conventional algorithm, the computation complexity of this proposed algorithm only increases a little and remains the same order. Simulations are carried out to verify the improvement of performance of our proposed algorithm.

This paper proposes three mathematical bounds of handover performance in CDMA system, Bound1 is the lower bound of hard handover(HHO) performance with variable handover thresholds, Bound2 is the lower bound of soft handover (SHO) performance and also the upper bound of HHO performance with variable handover thresholds, and Bound3 is the upper bound of SHO performance with variable handover thresholds. According to the bounds, the scope of handover performance is divided and limited. In order to form the mathematical basis of the bounds, this paper presents the analyzing methods and the final mathematical expressions of the outage probability in HHO and SHO. By simulating the expressions in the WCDMA (FDD) system, this paper concludes that the relevant expressions are proved to be correct, and it is more appropriate and accurate to utilize the expressions in this paper to evaluate the performance of HHO and SHO in a real CDMA system than Viterbi's (1994) estimates of HHO and SHO.

We propose a switched-beam smart antennas scheme which is based on the 2-dimensional searching of beams and channels, and analyze the signal to interference (SIR) performance of the system uplink when employing the scheme. The proposed scheme has a better performance compared with the traditional scheme of 1-dimensional singular searching of the beams and channels. It accords with the development of smart antennas in future mobile communication systems.

In this paper, a novel joint CDMA/RTDMA protocol for multimedia transmission in wireless networks is studied. In this scheme, the base station allocates terminals with code-slots instead of slots. Theoretical analysis of voice packet dropping rate and data delay are based on the M/M/n/m model and phase process respectively. Through simulation and numerical results, this new MAC protocol can provide multiple service QoS even under heavy load.

In this paper, we introduce a new solution to analyze performance of Space-Time Block Coding (STBC) under Rayleigh fading channels for CDMA multiuser environment. We consider a typical downlink CDMA system with N transmit antennas and M receive antennas. We derive a new expression of BER for STBC and compare it with conventional maximum ratio combination (MRC) technique having M*N diversity order. We find that STBC provides not only the same diversity gain as MRC, but additional coding gain. So STBC has better performance than MRC when taking the near-far situation into account.

A linear recursive "one-shot" decorrelator for asynchronous CDMA systems is developed. It has a lower complexity and better performance than existing "one-shot" decorrelators while eliminating all multiple access interference (MAI). This decorrelator does not exploit any signal energy information. Through simulation, this decorrelator is shown to be near-far resistant in both AWGN and fading channel.

To face the development of multimedia mobile communication with a large number of users, a novel method of active dynamic multiuser detection for WCDMA communication systems is proposed in this paper. It can reconfigure the detector dynamically according to different service requirements and integrated dynamic QoS of multi-access wireless channels. The active dynamic reconfiguration of the multiuser detector can satisfy the requirements of various ranges of bit error rate and robustness.

The performance and implementation of PRACH (physical random access channel) acquisition in WCDMA system is investigated. The analysis shows that the conventional methods are not satisfying. Thus we proposed the quasi-matched filter acquisition scheme of PRACH preamble which based on fast Hadamard transform. We implement this method by hardware in the practical WCDMA field trial system. The simulation and test results show that the proposed scheme achieves the following performance: the detection probability with E/sub b//N/sub 0/ =7 dB is not less than 95%, and the mean acquisition time is less than 1.33 ms.

We propose a new algorithm to realize STBC (space-time block coding) decoding with multipath components in a CDMA receiver. We construct a symbol-by-symbol detector directly utilizing multipath components to achieve better performance. Our proposed algorithm equivalently extends the number of receive antennas. We deduce the BER expression of our proposed algorithm, and we perform numerical results of BER performance.

In this paper, we present a M-ary MC-CDMA system for 4G which can support data rates up to 20 Mbps. In the transmitter, data bits are serial to parallel converted, then applying M-ary orthogonal modulation, the modulated symbol is spread using each chip of complex orthogonal codes. In a frequency selective slowly fading channel, we analyze the system performance of the downlink.

It is well known that the TDOA estimation technique has been widely used in many kinds of location systems, such as radar, sonar and GPS etc. But, because of its serious multipath propagation the cellular location system has much more difficulty in using TDOA than those traditional location-oriented systems mentioned. And so, looking for a new TDOA estimation model and algorithm that is robust and accurate in all kinds of propagation environments is an especially important task for cellular systems. This article combines multipath equalization and identification techniques and proposes a new model and algorithm for TDOA estimation in a cellular positioning system. Theory and computer simulation both prove that a simple estimation algorithm can obtain good estimation results in this model.

A spread spectrum (SS) modulation method of the forward channel in cellular systems is proposed. This method can be used to improve the transmitting properties of the forward CDMA channel with a given output power at the base station. It can map a number of forward CDMA signals onto a binary signal by orthogonally spreading sequences. The fundamental principle, performance and comparison with conventional SS modulation are discussed here.