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In this paper, the maximum signal-to-interference-plus-noise ratio (MSINR) beamforming problem in antenna-array CDMA systems is considered. In this paper, a modified MSINR criterion presented in a previous paper is interpreted as an unconstrained scalar cost function. By applying recursive least squares (RLS) to minimize the cost function, a novel blind adaptive beamforming algorithm to estimate the beamforming vector, which optimally combines the desired signal contributions from different antenna elements while suppressing noise and interference, is derived. Neither the knowledge of the channel conditions (fading coefficients, signature sequences and timing of interferers, statistics of other noises, etc.) nor training sequence is required. Compared with previously published adaptive beamforming algorithms based on the stochastic-gradient method, it has faster convergence and better tracking capability in the time-varying environment. Simulation results in various signal environments are presented to show the performance of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper investigates the features of a cellular geometry in code-division multiple-access (CDMA) systems with soft handoff and distinguishes controlling area of a cell from coverage area of a cell. Some important characteristics of the cellular configuration in soft handoff systems are used to propose a new design of efficient call admission control (CAC) in CDMA systems. Then, the paper constructs a continuous-time Markov chain (CTMC) model for CAC in CDMA with a soft handoff queue, obtains closed-form solutions, and thus develops loss formulas as performance indices such as the new blocking probability and the handoff dropping probability. In order to determine handoff traffic arrival rate, a fixed-point strategy is developed. Algorithms are also provided to stably compute loss probabilities and to determine the optimal number of guard channels. A new soft handoff scheme—eliminating pseudo handoff calls (EPHC)—is proposed to improve channel utilization efficiency based on mobility information. As an application of the loss formulas, the proposed modeling techniques are used to evaluate and compare the performance of conventional and proposed EPHC soft handoff schemes. Numerical results show the effectiveness of the proposed Markov chain models and the benefits of the new soft handoff scheme. [ABSTRACT FROM AUTHOR]

In this paper, the authors develop an analytical model to study the performance of a mobile low earth orbiting (LEO) satellite cellular network. The model assumes that the call duration has a gamma distribution and considers the effect of system parameters such as the number of channels per cell, the number of channels reserved for the handoff, and the cell residence time, on the teletraffic performance of the system. The quality of service (QoS) measures studied in this paper include new call blocking probability, handoff failure probability, premature call-termination probability (CTP), and call dropping probability (CDP). Based on the causal central limit theorem, the authors use a two-parameter gamma distribution to approximate the distribution of the sum of the residence times in the cells. The analytical model presented in this paper may be used with any call-holding-time distribution. The analytical results are validated by a computer simulation. [ABSTRACT FROM AUTHOR]

The bit-interleaved coded modulation (BICM) method is efficient in mitigating multipath fading by providing time diversity. In this paper, union bounds on the bit and packet error probabilities of the 81CM are derived. In the derivation, the authors assume the uniform interleaving of coded bits prior to mapping them onto the signal constellation. This results in a random distribution of the error bits in a codeword over the transmitted symbols. This distribution is evaluated, and the corresponding pairwise error probability is derived. Union bounds are functions of the distance spectrum of the channel code and the signal constellation used in the BICM system. The authors consider BICM systems operating over additive white Gaussian noise (AWGN), Rayleigh, Rician, and Nakagami fading channels. Results show that the new bounds are tight to simulation curves for different channel models. The proposed bounds are general for any coding scheme with a known distance spectrum. [ABSTRACT FROM AUTHOR]

A linear group-wise successive interference canceller in a synchronous code-division multiple-access system (CDMA) is considered in this paper. The proposed hybrid detector that combines successive and parallel cancellation techniques makes use of advantages offered by the two techniques. The convergence of the hybrid interference cancellation (HIC) detector is guaranteed by an adjustable parameter that depends upon the largest eigenvalue of the system's transition matrix. Since the largest eigenvalue is difficult to estimate, an upper bound is necessary for successful convergence. For this reason, a new upper bound for the maximum eigenvalue of the system's transition matrix was developed. Moreover, a new ordering and grouping algorithm that results in a higher convergence speed is proposed. Simulation results show that a significant improvement in performance is obtained using this technique. [ABSTRACT FROM AUTHOR]

The stall of delivering medium access control (MAC) layer data to the upper layer is a serious problem when a negative acknowledgement (NACK) control signal becomes an acknowledgement (ACK) signal, especially for a high-speed mobile terminal during handoff. Stall avoidance mechanisms aim to reduce such the transmission delay and keep in-sequence delivery of the MAC layer data to the upper layer. Recently, for providing high- speed downlink packet access (HSDPA) in the wideband code-division multiple access system, an indicator-based stall avoidance (ISA) mechanism was proposed to remove the nonrecoverable gap in the received out-of-sequence packets. In this paper, we derive the closed-form expression for the gap-processing time of the ISA mechanism when applying the multiprocess stop-and-wait (SAW) hybrid automatic repeat request (HARQ) mechanism. The derived analytical formulas can be used to understand performance tradeoffs between the gap-processing time and throughput in terms of various numbers of users and parallel processes when implementing the multiprocess SAW HARQ mechanism in the HSDPA system. [ABSTRACT FROM AUTHOR]

Multipath transport provides higher usable band- width for a session. It has also been shown to provide load balancing and error resilience for end-to-end multimedia sessions. Two key issues in the use of multiple paths are 1) how to minimize the end-to-end delay, which now includes the delay along the paths and the resequencing delay at the receiver, and 2) how to select paths. This paper presents an analytical framework for the optimal partitioning of real-time multimedia traffic that minimizes the total end-to-end delay. Specifically, it formulates optimal traffic partitioning as a constrained optimization problem using deterministic network calculus and derives its closed-form solution. Compared with previous work, the proposed scheme is simpler to implement and enforce. This analysis also greatly simplifies the solution to the path selection problem as compared to previous efforts. Analytical results show that for a given flow and a set of paths, a minimal subset can be chosen to achieve the minimum end-to-end delay with O(N) time, where N is the number of available paths. The selected path set is optimal in the sense that adding any rejected path to the set will only increase the end-to-end delay. [ABSTRACT FROM AUTHOR]

Resource allocation and call admission control (CAC) are key management functions in future cellular networks, in order to provide multimedia applications to mobiles users with quality of service (QoS) guarantees and efficient resource utilization. In this paper, we propose and analyze a priority based resource sharing scheme for voice/data integrated cellular networks. The unique features of the proposed scheme are that 1) the maximum resource utilization can be achieved, since all the leftover capacity after serving the high priority voice traffic can be utilized by the data traffic; 2) a Markovian model for the proposed scheme is established, which takes account of the complex interaction of voice and data traffic sharing the total resources; 3) optimal CAC parameters for both voice and data calls are determined, from the perspective of minimizing resource requirement and maximizing new call admission rate, respectively; 4) load adaption and bandwidth allocation adjustment policies are proposed for adaptive CAC to cope with traffic load variations in a wireless mobile environment. Numerical results demonstrate that the proposed CAC scheme is able to simultaneously provide satisfactory QOS to both voice and data users and maintain a relatively high resource utilization in a dynamic traffic load environment. The recent measurement-based modeling shows that the Internet data file size follows a lognormal distribution, instead of the exponential distribution used in our analysis. We use computer simulations to demonstrate that the impact of the lognormal distribution can be compensated for by conservatively applying the Markovian analysis results. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of two control parameters of the Universal Mobile Telecommunications System (UMTS) handoff algorithm on the total peak base station (BS) transmit power required per mobile station (MS) to satisfy a prescribed outage probability. Denoting the set of BSs supporting an MS in soft handoff (SH) as the active group, the first parameter n is the maximum allowed size of the active group. The second, denoted r, is the upper limit on the difference between the path loss of the dominant BS and that of any other member of the active group, where the term "dominant" refers to the BS with the lowest path loss to the MS. It was assumed that the MS is equipped with a Rake receiver capable of performing "maximal ratio combining" of the signals it receives from the transmitting BSs. General analytical derivations along with results derived for specific situations through numerical integration are presented. [ABSTRACT FROM AUTHOR]

In this paper, we present a unified approach for the computation of the outage probability, the level crossing rate (LCR), and the average outage duration (AOD) of selection combining (SC) in the presence of multiple cochannel interferences and under both minimum signal-to-interference ratio (SIR) and desired signal power constraints. We consider three selection algorithms, namely, 1) the best signal power algorithm; 2) the best SIR algorithm; and 3) the best total power (desired plus interference) algorithm. As a specific application example, we analyze the three algorithms for a low-complexity dual-branch SC receiver subject to multiple interferers over Rayleigh fading channels. When applicable, the new results are compared to those previously reported in the literature dealing with the outage probability, AOD, and LCR of 1) interference-limited systems and 2) power-limited systems. Numerical examples show that the minimum desired signal power constraint induces a floor to the outage probability, AOD, and LCR performance measures. They also show that the best SIR algorithm provides the best outage probability and AOD performance for low average SIR. On the other hand, the best signal power algorithm and the best S + I algorithm outperform the best SIR algorithm for high average SIR. It is also shown that the best SIR algorithm tends to have more outage level crossings. [ABSTRACT FROM AUTHOR]

This paper presents an elegant technique for solving the channel assignment problem (CAP) for second generation (2G) cellular mobile networks, where channel allocation is made on a quasi-fixed basis and all sessions are connection oriented. It first maps a given CAP P to a modified coalesced CAP P' on a smaller subset of cells of the network, which appreciably reduces the search space. This helps to solve the problem P' by applying approximate algorithms very efficiently, reducing the computing time drastically. This solution to P' is then used to solve the original problem P by using a modified version of the forced assignment with rearrangement (FAR) operation reported by Tcha et al. (IEEE Trans. Veh. Technol., vol. 49, p. 390, 2000). The proposed technique has been tested on well-known benchmark problems. It has produced optimal solutions for all cases with an improved computation time. For instance, it needs only around 10 and 20 s (on an unloaded DEC Alpha station 200 4/233) to get an optimal assignment for the two most difficult benchmark problems 2 and 6, respectively, with zero call blocking, in contrast to around 60 and 72 s (on an unloaded Sun Ultra 60 workstation) reported by Ghosh et al. Moreover, as a by-product of this approach, there remain, in general, many unused or redundant channels that may be used for accommodating small perturbations in demands dynamically. [ABSTRACT FROM AUTHOR]

Sensor networks are comprised of nodes with minimal baseband and RF functionalities. In such networks, it is assumed that a source sensor communicates with a target sensor over a number of relaying sensors by utilizing distributed low- complexity space-time encoding techniques, hence the resulting communication scenario is a generalized form of orthogonalized multiple-input multiple-output (MIMO) channels. The contributions of this paper are the derivation of the Shannon capacity in terms of natural units per second per Hertz for such space- time encoded distributed communication scenarios. Closed-form capacity expressions are derived for ergodic flat-fading Rayleigh and Nakagami channels, as well as the communication-rate outage probabilities for aforementioned channels. It is shown that the distributed Alamouti scheme yields the best performance over ergodic channels. In the case of nonergodic channels, the 3/4-rate sporadic space-time block code (STBC) is shown to give optimum performance. Finally, Monte Carlo simulations are used to assess the performance of distributed multistage sensor networks. It is shown that notable power savings can be achieved, compared to the traditional single-link sensor networks. [ABSTRACT FROM AUTHOR]

The wireless personal area network (WPAN) is designed for short-range connectivity among fixed or portable moving devices. The ultra-wideband (UWB) technology is being defined as the physical-layer (PHY) support for the high-rate WPAN. At medium access control (MAC) layer of the WPAN, a delayed acknowledgment (Dly-ACK) or burst-ACK (B-ACK) scheme is introduced to improve the channel utilization by reducing the overhead of ACK. In this paper, the authors first study the delay performance of the Dly-ACK scheme. An analytical model is developed for the Dly-ACK mechanism, and the delay is decomposed into queuing delay and delivery delay. These delay metrics are derived, and some important observations are obtained. In particular, there exists an optimal burst size, which is determined by the input traffic load and is very insensitive to the channel error rate within a normal error-rate range. It is also demonstrated that Dly-ACK cannot work properly if the burst size is fixed. The authors then propose a dynamical Dly-ACK scheme that can adaptively change its burst size according to the queue buffer size. Simulation results show that the dynamical scheme can improve the delay performance significantly. [ABSTRACT FROM AUTHOR]

This paper proposes a new linear blind multiuser detection based on widely linear (WL) signal processing. The received signal and its complex conjugate are separately filtered and the results are linearly combined. The WL maximum/minimum (max/min) mean-output-energy (MOE) receiver is derived by applying the modified cost function. It is shown that a performance gain can be attained for the improper direct-sequence code division multiple access (DS/CDMA) signal, due to the additional in- formation contained in pseudocovariance matrix of observations. The adaptive implementation with acceptable complexity is also developed. Computer-simulation results show that a significant performance gain is obtained over the other classical methods. [ABSTRACT FROM AUTHOR]

In this paper, the authors propose selective map- ping (SLM) and partial transmit sequences (PTS) employing an intermodulation distortion (IMD)-reduction strategy to improve the error-probability performance of nonlinearly distorted orthogonal frequency division multiplexing (OFDM). In particular, the authors consider two IMD-reduction criteria: One requires knowledge of nonlinearity parameters, whereas the other does not. Simulation results demonstrate that in the presence of non-linearities, OFDM systems using SLM or PTS with either of the IMD-reduction strategies perform better than those with peak- to-average power ratio (PAPR) or the recently proposed excess power (EP)-reduction strategies. Furthermore, the error-probability performance of the IMD-reduction technique that exploits knowledge of nonlinearity parameters is only slightly better than that of the technique that does not. Additionally, simulation results also demonstrate that the average out-of-band power generated by the IMD-reduction strategies is similar to that generated by PAPR or EP reduction. [ABSTRACT FROM AUTHOR]

Orthogonal code-hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to increase the number of allowable downlink channels in code division multiple access (CDMA) systems. OCHM is expected to compensate for a lack of codewords in future communication systems. In CDMA systems including OCHM, system capacity is limited by the number of codewords and power (or interference), and the maximum system capacity is determined by a stronger limitation between them. Call blockings due to power limitation may occur firstly if downlink channels demand large Eb/I0 values and a high-channel activity. On the other hand, code limitation may occur prior to power limitation in CDMA. The maximum system capacities determined by both code and power limitations must be known, even in OCHM. However, previous studies on OCHM system capacity focused only on increasing the number of multiplexed users with no consideration of the power limitation. In this paper, the overall system capacity of OCHM considering both code and power limitations was evaluated. For this analysis, the transmission chip energy of base station (BS) and inner/outer-cell interference is mathematically derived in a multicell and multiuser environment. The downlink system capacity for OCHM is larger than for orthogonal code division multiplexing (OCDM) as other cell interference (OCI), mean channel activity, and the required Eb/I0 value decrease. [ABSTRACT FROM AUTHOR]

Referring received signal strength (RSS) to a signal propagation model to find user location is one of the most promising strategies in wireless communications. This paper develops a simple method based on relative signal-strength measurements, that is, the differences in stationary signal strength measured at the user location from multiple base transceiver stations (BTSs). The stationary signal strength is the averaged RSS and also is a stationary Gaussian process. In using this method, it is vitally important to confirm that some uncertain propagation parameters can be canceled out while a signal propagation model is merged into our method for locating users. In this way, the differences in stationary signal strength lead to two solutions: One is the distance difference between pairs of BTSs, and the other is the distances from the user location to the multiple BTSs. Consequently, the hyperbolic positioning algorithm due to the distance-difference solution and the circular positioning algorithm due to the distances solution can be presented, respectively. Afterward, some experimental results were drawn from a field trial in a real propagation environment. Results show that the hyperbolic and circular positioning algorithms can locate the user to within about 350 and 300 m in 67 percentile, respectively. Compared with the numerical result reported in the literature on existing methods based on RSS only, our method is superior. Despite the result not meeting Federal Communications Commission (FCC) requirements, this method proved to be sufficiently simple and efficient in terms of the computation at burden and network signaling load. [ABSTRACT FROM AUTHOR]

Employing multiple antennas at the transmitter is a well-established technique for providing diversity advantage in wireless systems. Transmit beamforming relies on the assumption of current channel knowledge at the transmitter, which is unrealistic when the forward and reverse links are separated in frequency. One solution to this problem is for the receiver to send a small number of feedback bits that convey channel information to the transmitter. Feedback design techniques have been proposed over the past few years, but they were derived using the assumption of spatially uncorrelated Rayleigh fading. This correspondence addresses the design of limited feedback beamformers when the channel is correlated. [ABSTRACT FROM AUTHOR]

Log-likelihood ratio (LLR) conversion schemes are proposed to mitigate the effect of collisions (or perforations) that occur in orthogonal code-hopping multiplexing (OCHM), which was previously proposed to accommodate more downlink channels than the number of orthogonal codewords. The proposed LLR conversion schemes greatly reduce the required SNR in channel decoding even when the perforation probability is high. The perforation probability in some LLR conversion schemes is estimated and several estimation methods are proposed. An LLR conversion scheme without estimation of the perforation probability is also proposed to avoid accurate estimation. The performance of the proposed schemes is evaluated by simulation in terms of the required Eb/N0 for a 1% block error rate (BLER). [ABSTRACT FROM AUTHOR]

In this contribution, the capacity of multiple-input multiple-output (MIMO) systems using multidimensional phase- shift keying/quadratic-amplitude modulation signal sets is evaluated. It was shown that transmit diversity is capable of narrowing the gap between the capacity of the Rayleigh-fading channel and that of the additive white Gaussian noise channel. However, because this gap becomes narrower when the receiver diversity order is increased, for higher order receiver diversity, the performance advantage of transmit diversity diminishes. A MIMO system having full multiplexing gain has a higher achievable throughput than the corresponding MIMO system designed for full diversity gain, although this is attained at the cost of a higher complexity and a higher signal-to-noise ratio. The tradeoffs between diversity gain, multiplexing gain, complexity, and bandwidth are studied. [ABSTRACT FROM AUTHOR]

Phase-sweep transmit diversity (PSTD) has been widely studied in 3G1X and Universal Mobile Telecommunications Systems (UMTS) for its performance gain and simplicity. However, conventional PSTD systems are designed based on a single-sweeping beam, and only one user is selected for transmission at any time. Therefore, it fails to fully exploit the available spatial degree of freedom. In this study, a novel spatial-multiplexing phase-sweep transmit diversity (SM-PSTD) scheme with partial feedback mobile-assisted scheduling is being proposed. The down- link performance (system capacity and proportional fairness) of a multiantenna base station has been its focus. The spatial-channel sweeping facilitates the multiuser selection diversity between users, while the spatial multiplexing significantly enhances the system capacity. As the number of transmit antennas nT is increased, the SM-PSTD system performance is gradually limited by the multiuser interference because it is more and more difficult to find a set of users perfectly orthogonal within the nT spatial channels. Yet, the multiuser interference could be reduced by increasing the number of active users K in the system. Asymptotically, at large nT and K, it shows that the system capacity scales linearly instead of logarithmically with respect to the transmitted power. [ABSTRACT FROM AUTHOR]