Throughput-optimal cross-layer resource allocation in DS-CDMA systems with Nakagami multipath fading

In CDMA systems, outer loop power control (OLPC) determines the target value of SNR at the receiver, mostly by using look-up tables to map bit error rates (BERs) to SNRtargets. In this contribution, transmission delay and packet loss rate constraints in the data link layer (DLL) are invoked in order to determine the optimum outer loop SNR-target setpoint analytically, according to the number of active users in cell. Optimality is, in this sense, the maximization of system throughput. Using the optimum SNR-target, the optimal spreading factor is determined. Subsequently, the joint optimization of outer loop SNR-target and variable spreading factor (VSF), at the physical(PHY)-layer, with truncated automatic repeat request (ARQ) error control mechanism at the data link layer are proposed. Our scheme is compared with 'constant SNR-target' and 'PHY-layer based variable SNR-target' cases under continuous power and rate variation to show (analytically and by simulations) the achievable gain through the coupling of physical and data link layers parameters.

Selection cooperation is an effective solution for cooperative communications and the automatic repeat request (ARQ) protocol can provide additional diversity gain for wireless networks. In this work, considering a large network where direct transmissions only exist in the neighbors of each node, we investigate an improved diffusion selection cooperation protocol integrated with ARQ, and taking into account of the case that neighbors of the destination join cooperation at each ARQ retransmission. As a result, it can provide a complete insight into the performance analysis of the improved protocol. Moreover, the exact diversity-multiplexing-delay (D-M-D) tradeoff for each round of retransmission is derived. And the simulation results validate the accuracy of the improved scheme.

ARQ (Automatic-Repeat-Request) protocols are used in communication applications to ensure reliable delivery of packetized data in the correct sequence. The major used protocols are: Stop and Wait (SW), Go Back N, and Selective Repeat (SR). In this paper we continue studying and measuring the performance of Automatic Repeat Request (ARQ) protocols. ARQ protocols are used at Data Link Control (DLC) sub layer of Data Link Layer (DLL) to achieve error control and provide smooth and reliable transmission between nodes. They use acknowledgements and timeouts to satisfy reliable data transmission over noisy channels. This paper analyses the service time distributions of Selective Repeat ARQ protocol used in transmission of short messages over noisy channels. The system is operated according to SW protocol in the message level, while packets in each message are transmitted according to $\mathrm{S}\mathrm{R}_{\infty}$ ARQ protocols. The system is modeled as a stochastic process where it includes senders and receivers. We consider applying $\mathrm{S}\mathrm{R}_{\infty}$ with connection-oriented transmission. The Probability Generating Function of service time is calculated and first and second moments of the service time are derived.

This paper aims at clarifying the role of the outer loop power control for CDMA satellite systems with on-board power constraints. If the inner loop of the power control is perfect, the channel turns into a AWGN channel and there is no need of the outer loop. In satellite CDMA sytsems, due to the longer propagation delay with respect to a terrestrial system, the inner loop of power control is only partly able to track power variations due to fast fading. Moreover, the Rice factor, which characterizes the channel statistics, can widely vary even if the user does not move but just because of the change of the elevation angle. Because of that, a wide range of target SNIR (and larger than in typical terrestrial systems) may be necessary to get the same BER performance. Therefore, the outer loop power control turns out to be essential to minimize the dynamic of the power link margins and avoid capacity degradations induced by the systematic use of static link margins.
\nA semi-analytical model for the capacity evaluation has been developed, which is specifically intended for the power-limited satellite-to-mobile link with multi satellite reception. We found that the capacity gain with respect to pure SNIR-based strategy (i.e. only inner loop) can reach the 40% of the total capacity in a single reception scheme. A smaller, but still noticeable capacity gain of the order of 20-30% is observed in the presence of satellite diversity. Therefore, any dimensioning of CDMA satellite systems should neglet this component of the power control.

This paper proposes a novel framework for the cross-layer analysis and design of wireless networks combining adaptive modulation and coding (AMC) at the physical layer with an automatic repeat request (ARQ) protocol at the data-link layer. Most previous works rely on first-order amplitude-based finite-state Markov chains (AFSMCs) to model the physical layer. It is shown that these models present several deficiencies that could compromise the design of higher layer protocols. Thus, a physical-layer first-order 2-D Markov model using both the amplitude and the rate of change of the fading envelope is presented. Based on this multidimensional physical-layer Markov model, the quality-of-service (QoS) performance at the data-link layer is investigated through the use of two different approaches. The first one relies on an analytical framework based on a discrete-time Markov chain (DTMC) that jointly describes the statistical behavior of the arrival process, the queueing system, and the physical layer. The second one is based on the effective-bandwidth and effective-capacity theories. Both the DTMC-based and the effective-bandwidth/capacity-based approaches are analyzed and compared in combination with our proposed physical-layer first-order 2-D Markov model in a cross-layer design aiming to satisfy the required average packet loss probability constraint by maximizing the average throughput of the system. Numerical results show that our proposed framework represents a significant improvement over previous models.

Outer loop power control (OLPC) is also an important radio resource management (RRM) algorithm in dedicated channels of code division multiple access (CDMA) systems. Proposed is a new OLPC algorithm that also takes HARQ into consideration. The proposed algorithm can guarantee the QoS and help the system to greatly decrease average physical layer delays with similar relative throughput to the conventional algorithm.

In this work, Automatic-Repeat-Request (ARQ) and Maximal Ratio Combination (MRC), have been jointly exploited to enhance the confidentiality of wireless services requested by a legitimate user (Bob) against an eavesdropper (Eve). The obtained security performance is analyzed using Packet Error Rate (PER), where the exact PER gap between Bob and Eve is determined. PER is proposed as a new practical security metric in cross layers (Physical/MAC) security design since it reflects the influence of upper layers mechanisms, and it can be linked with Quality of Service (QoS) requirements for various digital services such as voice and video. Exact PER formulas for both Eve and Bob in i.i.d Rayleigh fading channel are derived. The simulation and theoretical results show that the employment of ARQ mechanism and MRC on a signal level basis before demodulation can significantly enhance data security for certain services at specific SNRs. However, to increase and ensure the security of a specific service at any SNR, adaptive modulation is proposed to be used along with the aforementioned scheme. Analytical and simulation studies demonstrate orders of magnitude difference in PER performance between eavesdroppers and intended receivers.

In this paper a novel network architecture employing space diversity for Wireless Sensor Networks (WSN) is proposed. A simulation study has been carried out to evaluate performance of such WSN employing space diversity in terms of optimal transmit power. Optimal transmit power is the minimum power required to sustain the network connectivity while maintaining a predefined maximum tolerable Bit Error Rate (BER) in WSN. Optimization of transmit power is of great importance in WSN since sensor nodes are battery driven and optimization helps to increase battery life by reducing inter node interference significantly. The impact of Maximal Ratio Combining (MRC) based space diversity on optimal transmit power is investigated in presence of Rayleigh fading. Use of MRC space diversity in Rayleigh fading channel shows a significant reduction in optimal common transmit power. Average number of retransmissions for successful delivery of a packet is also evaluated considering an infinite Automatic Repeat Request (ARQ) scheme.

In this article, we propose a cross-layer approach to maximize the throughput efficiency of the hybrid automatic repeat request (HARQ) protocol while guaranteeing ultrareliable communication (URC). The study combines adaptive modulation and coding and power control, at the physical layer, with automatic repeat request (ARQ)/HARQ at the data-link layer. The proposed optimization approach, based on genetic algorithms, allows a judicious allocation of the available energy budget and a suitable modulation and coding scheme (MCS) choice while keeping the same energy budget. For a given signal-to-noise ratio (SNR), a vector of energy and an MCS are modeled as one individual. The individuals with the highest throughput efficiency are selected to be used in generating the next population through crossover of the survivals and mutation. The individual with the highest throughput efficiency in the last population presents the solution offering the optimized parameters used in the packet transmission. We compare our solution to an existing one that exploits Lagrange multipliers. The results show that the proposed genetic algorithm based solution ensures URC with packet erasure probability less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$10^{-5}$</tex-math></inline-formula> from SNR values of 7 and 13 dB in static and fading channels, respectively.

Loss performance model for wireless channels with autocorrelated arrivals and losses

A novel strategy for semi-blind spatio-temporal equalization and multiuser detection for short-burst asynchronous DS-CDMA systems is proposed. The technique is based on first performing channel identification (through a semi-blind subspace-based algorithm) as an aid for semi-blind equalization (via the constant modulus algorithm (CMA)). This two step process allows us to improve upon the traditional training-based least squares (LS) estimator by adding the constant modulus and cyclostationary properties of communication signals. Simulation results comparing the performance of our algorithm with regularized LS estimators (both training-based and semi-blind) for different amounts of spatial-diversity, number of active users and burst lengths indicate a significant reduction in the required number of training symbols. Application of this work is in the reverse-link of third generation DS-CDMA systems.

To minimize the terminal's transmission power in bursty uplink traffic conditions, the evolved high-speed uplink packet access (HSUPA) concept in 3GPP WCDMA includes a feature known as dedicated physical control channel (DPCCH) gating. We present here a detailed link level study of gating from a link efficiency (LE) perspective; LE being expressed in bits per second per Watt. While the overall gain mechanisms of gating are well known, we show how special challenges related to discontinuous enhanced dedicated channel (E-DCH) transmission can be addressed for high link and system performance. We consider the E-DCH performance degradation caused by gating on other radio procedures relying on the DPCCH, such as inner and outer loop power control. Our studies show that gating is beneficial for both for 2 and 10 ms transmission time intervals. The gains in terms of LE with a vehicular A 30 kmph channel are in the range of 4-5 dB for a bit rate of 32 kbps and an E-DCH activity factor of 0.1. For bit rates higher than 1 Mbps and an activity factor of 0.25, the gains are close to zero or even negative.

Advanced algorithms have become available in recent years that can reliably measure the speech quality as ‘perceived’ by humans. The benefits of applying the perceptual quality measures obtained using these algorithms in the outer loop power control (OLPC) of the Third Generation Universal Mobile Telecommunication System (3G UMTS) are studied. It is shown that 20% capacity improvement compared to the use of conventional measures can be achieved, while an adequate and uniform speech quality is maintained.

A cooperative automatic repeat request (ARQ) scheme is proposed for cognitive radio networks with full duplex capability. Its performance is studied for ARQ and hybrid ARQ (HARQ) modes, in terms of data link layer packet error rate (PER) and the primary and secondary throughputs. It is shown that activity of the secondary network during primary’s retransmission does not affect primary’s performance in ARQ mode, and would even improve it in HARQ mode.

The higher data rate of mobile communications has been required for various multimedia services. In DS-CDMA system, one of the solutions to increase the throughput is to use multicode. However, multipath channel destroys the orthogonality of spreading codes, which causes the intercode interference (ICI). ICI gives severe effect on multicode DS-CDMA for BER performance. Conventionally, multicode DS-CDMA system uses the Rake receiver with turbo code, which cannot overcome error floor caused by ICI. In this paper, we propose frequency domain turbo equalization based on minimum mean squared error (FDTE-MMSE) for multicode DS-CDMA in frequency selective channel and evaluate its BER performance by computer simulation. The simulation results show that FDTE-MMSE gives much better performance than the Rake receiver with turbo code in multipath length L > 1.