Spatially and temporally correlated MIMO channels: modeling and capacity analysis

Wireless communication systems employing multiple antennas at both the transmitter and receiver have been shown to offer significant gains over single-antenna systems. Recent studies on the capacity of multiple-input-multiple-output (MIMO) channels have focused on the effect of spatial correlation. The joint effect of spatial and temporal correlation has not been well studied. In this paper, a geometric MIMO channel model is presented, which considers motion of the receiver and nonisotropic scattering at both ends of the radio link. A joint space-time cross-correlation function is derived from this model and variates with this joint correlation are generated by using the vector autoregressive stochastic model. The outage capacity of this channel is considered where the effects of antenna spacing, antenna array angle, degree of nonisotropic scattering, and receiver motion are investigated. When n transmit and n receive antennas are employed, it is shown that the outage capacity still increases linearly with respect to n, despite the presence of spatial and temporal correlation. Furthermore, analytical expressions are derived for the ergodic capacity of a MIMO channel for the cases of spatial correlation at one end and at both ends of the radio link. The latter case does not lend itself to numerical evaluation, but the former case is shown to be accurate by comparison with simulation results. The proposed analysis is very general, as it is based on the transmit and receive antenna correlations matrices.     

Simple stopping criterion for turbo decoding

A simple and effective criterion for stopping the iteration process in turbo decoding with negligible degradation of the error performance is presented. The new, improved hard-decision-aided (IHDA) extends the existing hard-decision-aided (HDA). Unlike the HDA, it requires no extra data storage, while achieving similar performance in terms of the BER and average number of iterations     

Performance evaluation of high rate space?time trellis-coded modulation using Gauss?Chebyshev quadrature technique

The performance analysis of high rate space-time trellis-coded modulation (HR-STTCM) using the Gauss-Chebyshev quadrature technique is presented. HR-STTCM is an example of space-time codes that combine the idea used in trellis coded modulation (TCM) design that is signal set expansion and set partitioning into its construction. HR-STTCM construction is based on the concatenation of an outer TCM encoder and inner space-time block code. This paper evaluates the exact pairwise error probability of HR- STTCM based on the Gauss-Chebyshev quadrature formula. Comparison of numerical and simulation results shows that the proposed method is accurate. The method used is shown to be computationally simpler than those in the literature.     

An improved decoding algorithm for finite-geometry LDPC codes

In this letter, an improved bit-flipping decoding algorithm for high-rate finite-geometry low-density parity-check (FG-LDPC) codes is proposed. Both improvement in performance and reduction in decoding delay are observed by flipping multiple bits in each iteration. Our studies show that the proposed algorithm achieves an appealing tradeoff between performance and complexity for FG-LDPC codes.     

AWGN信道中的超正交卷积Turbo码的性能

超正交卷积适合于扩频通讯应用.Petri 提出了超正交卷积Turbo码 (Superorthogonal Convolutional Turbo Code ,SCTC)[1],由于带宽的扩展,这类码的性能比一般的Turbo码好.推导了一般SCTC 码的构造,同时导出了存储单元分别为2,3的SCTC的转移函数.最后分别给出了AWGN信道下SCTC码的误码率性能上限,计算机模拟的max-log-MAP和SOVA译码算法的误码率性能.     

Channel assignment scheme in clustered multichannel cognitive radio networks with outdated CSI over Rayleigh fading channels

This work investigates channel assignment for cooperative spectrum sensing in multichannel cognitive radio networks, where the heterogeneity of primary user (PU) activity and the effect of varying channel condition on the received signal‐to‐noise ratio during cluster formation are considered. With the objective to minimize interference to the PU while enhancing multiple spectrum utilization of the secondary user (SU), an overlapping cluster‐based assignment is formulated into a nonlinear integer optimization problem. To obtain an efficient solution, the nonlinear integer problem is transformed into a mixed integer linear problem, based on which, this paper proposes an exact solution and then two new heuristic algorithms for suboptimal solutions, respectively. Furthermore, a comparative study of four different cluster head selection schemes with respect to their performance in cooperative spectrum sensing, under cluster's heterogeneity in terms of SUs distribution relative to PU transmitter location is presented. Based on the study, a robust cluster head selection scheme is proposed. Simulation results show that good sensing performance and increased opportunistic spectrum utilization in multichannel cognitive radio networks are two sides of a coin that depend on the ratio of the SUs to the number of PU channels. How far away the PU is from the cluster center is also seen to be key in the optimal selection of cluster heads in cooperative spectrum sensing.     

Spread‐spectrum CDMA packet radio MAC protocol using channel overload detection and blocking

An analytical and simulation performance evaluation is presented for a multi‐access protocol for a data packet radio network with a limited user capacity. The network employs direct‐sequence code division multiple access (DS‐CDMA) in a centralised channel load‐sensing scheme with channel overload (collision) detection and blocking via a separate ancillary channel state information broadcast system. Traffic models that incorporate both a finite population and an infinite population and variable length data messages are considered. Results show that an improved throughput/delay performance can be obtained by implementing a channel overload detection (message dropping) scheme as well as a channel overload avoidance (message blocking) scheme. The channel overload threshold β is fixed at the system's maximum user capacity whereas it is shown that the overload avoidance blocking threshold α should be variable and dependent on the mean message arrival rate. This revised version was published online in July 2006 with corrections to the Cover Date.     

An Ensemble of Iteratively Decodable Codes Constructed Based on a Superposition Method

In this paper, the construction of new families of error-correcting codes adapted from Boutros and Lentmaier's generalized low-density (GLD) codes, which we called generalized irregular low-density (GILD) codes, is investigated. By introducing irregular base matrices, significant improvements on Boutros and Lentmaier's results are achieved. Two cases are considered; in the first case, the same constituent code is used, and in the second case, different constituent codes are used. It is proved by an ensemble performance argument that these codes exist and are asymptotically good in the sense of the minimum-distance criterion. It is also proved that the performance of GILD codes approaches the binary symmetric channel capacity limit. Iterative decoding of GILD codes for communication over an additive white Gaussian noise channel is also studied. The high flexibility in selecting the parameters of GILD codes and their better performance and higher rate make them more attractive than GLD codes, and hence, suitable for small and medium block lengths forward-error-correcting schemes. Comparisons of simulation results between some GILD codes and some good low-density parity-check codes show very close performances     

Nonclassical traffic modeling and performance analysis of cellularmobile networks with and without channel reservation

We present a two-moment performance analysis of cellular mobile networks with and without channel reservation. Unlike classical analysis where handoff traffic is modeled as Poisson, we characterize handoff traffic as a general traffic process and represent it using the first two moments of its offered traffic. We empirically show that handoff traffic is a smooth process under negative exponential channel holding times. We also show how one may determine customer-oriented grade-of-service parameters such as new-call blocking, handoff call blocking, and forced termination probability under the two-moment representation of traffic offered to each cell. We present extensive results validating our analysis. We compare the performance of the proposed two-moment analysis with classical single-moment analysis and simulation results. Our simulation employs five different mobility models. We show that our proposed model outperforms the existing analytical method when compared to simulation results employing all five mobility models     

A Hybrid Token-CDMA MAC Protocol for Wireless Ad Hoc Networks

Token-passing medium access control (MAC) protocols are gaining interest among wireless ad hoc network researchers as they provide unrivaled advantages over the existing IEEE 802.11 standards. This paper introduces a hybrid token-code division multiple access (CDMA) MAC protocol that is based on a token-passing scheme with the incorporation of CDMA. With its unique CDMA feature, the proposed MAC is able to support multiple simultaneous transmissions. The proposed protocol provides both quality of service (QoS) and high network resource utilization while ensuring the stability of the network. This paper examines the performance of the proposed MAC scheme by simulation and compares its performance against that of other MAC protocols that have appeared in the literature. Simulation results demonstrate that our proposed MAC scheme is effective in decreasing the packet delay and significantly shortens the length of the queue. The input traffic model used in the simulation is a two-state Markov-Modulated Poisson Process (MMPP). The data rate QoS is enforced by implementing a modified leaky bucket mechanism in the proposed MAC scheme. The simulation also takes into account channel link errors caused by the wireless link by implementing a multilayered Gilbert-Elliot model.