Delay-bounded packet scheduling of bursty traffic over wireless channels

In this paper, we study minimal power transmission of bursty sources over wireless channels with constraints on mean queuing delay. The power minimizing schedulers adapt power and rate of transmission based on the queue and channel state. We show that packet scheduling based on queue state can be used to trade queuing delay with transmission power, even on additive white Gaussian noise (AWGN) channels. Our extensive simulations show that small increases in average delay can lead to substantial savings in transmission power, thereby providing another avenue for mobile devices to save on battery power. We propose a low-complexity scheduler that has near-optimal performance. We also construct a variable-rate quadrature amplitude modulation (QAM)-based transmission scheme to show the benefits of the proposed formulation in a practical communication system. Power optimal schedulers with absolute packet delay constraints are also studied and their performance is evaluated via simulations.     

TCP performance over wireless MIMO channels with ARQ and packet combining

Multiple-input multiple-output (MIMO) wireless communication systems that employ multiple transmit and receive antennas can provide very high-rate data transmissions without increase in bandwidth or transmit power. For this reason, MIMO technologies are considered as a key ingredient in the next generation wireless systems, where provision of reliable data services for TCP/IP applications such as wireless multimedia or Internet is of extreme importance. However, while the performance of TCP has been extensively studied over different wireless links, little attention has been paid to the impact of MIMO systems on TCP. This paper provides an investigation on the performance of modern TCP systems when used over wireless channels that employ MIMO technologies. In particular, we focus on two representative categories of MIMO systems, namely, the BLAST systems and the space-time block coding (STBC) systems, and how the ARQ and packet combining techniques impact on the overall TCP performance. We show that, from the TCP throughput standpoint, a more reliable channel may be preferred over a higher spectral efficient but less reliable channel, especially under low SNR conditions. We also study the effect of antenna correlation on the TCP throughput under various conditions.     

Performance of CDMA random access systems with packet combining in fading channels

We analyze the system performance of code-division multiple-access (CDMA) random access systems with linear receivers and packet combing in multipath fading channels. Both slotted and unslotted CDMA systems with random spreading codes are considered. The analysis is based on large systems in which both the offered load and the processing gain tend to infinity but their ratio is fixed. It is relatively easy to characterize the traffic in such large systems, which enables us to derive the system throughput and average delay. From the analysis results, it is observed that multiuser detection and packet combining substantially improve the system performance.     

A connection control strategy for bursty sources in broadband packet networks

This paper proposes an admission strategy for connection-oriented services at the access node of a broadband integrated packet network based on asynchronous transfer mode. Based on an estimate of the probability of cell loss and in the absence of buffering, we determine the number of sources from different classes of bursty traffic which can be accepted. The parameters which are used to describe the traffic sources are average bit rate and peak bit rate. We will evaluate the cell loss estimate for homogeneous and heterogeneous cases. Furthermore, we will examine the variation of this estimate as the average to peak ratio changes. The estimate is an upper bound for the probability of cell loss. Based on this upper bound simple and robust allocation of resources to bursty sources can be developed. The proposed strategy can be implemented using simple computations or via a look-up table to determine admission or denial of an incoming call and therefore allocating the required capacity. The procedure results in efficient use of the bandwidth, ensuring the desired service quality for connection-oriented services and results in proactive control of network congestion.     

Buffer sizing for synchronous self-routeing broadband packet switches with bursty traffic

Previous studies on the performance of synchronous self-routeing packet switches have assumed that the input traffic is random, i.e. there is no correlation between adjacent packet arrivals. This assumption is generally not valid in the data communication environment (e.g. host-to-host communication) where a file transfer usually generates a string of correlated packets. The consequence is that the random traffic assumption greatly underestimates the buffer requirement of the switch. In this paper, we model each input traffic stream as a binary source as a first step to understand the performance of a packet switch in a bursty traffic environment. We found that, given a fixed traffic load (or switch utilization), the required buffer size increases linearly as the burstiness index (the average burst length) of the traffic increases. In addition, the required buffer size is more sensitive to the burstiness of the traffic, when the average traffic load is higher and when the packet loss requirement is more stringent. Initial applications of broadband packet switches are likely to be the interconnections of LANs and hosts. The results of the study indicate that the high burstiness in certain broadband traffic significantly reduces the allowable switch utilization, given a fixed amount of buffers. To increase the switch utilization, an appropriate congestion control mechanism needs to be implemented.     

MIMO slotted ALOHA systems with collision resolution and truncated HARQ transmission and combining

In this paper, we investigate throughput and delay enhancement for two multi-user multiple-input multiple-output (MIMO) systems one with space-time block coding (STBC), the other with spatial multiplexing (SM) at the transmitter. Users operate using the slotted ALOHA (SA) protocol to access the wireless channel resulting in a high probability of collision. For both systems, we consider the uplink scenario, and we propose to recover the collided packets with spatial successive interference cancelation (SSIC) and a protocol for retransmission and combining of unsuccessfully received collided packets applying a truncated Hybrid Automatic Repeat reQuest (HARQ) scheme. For the first system, we propose to use channel realizations of collided packets as different signatures to separate them. Moreover, we propose a solution for the problem when the received powers are comparable. For this system, we note that the orthogonality of the STBC matrix allows the use of a simple linear processing step for the initialization of SSIC. For the SM multi-user system, the separation of collided packets is based on V-BLAST processing and SSIC. We also propose how to combine retransmitted packets. For both systems, we evaluate the block error rate, the throughput, and the delay. A comparison is done with the single-user case and with other receivers proposed in the literature.     

On rate control of packet transmission over fading channels

In error controlled packet reception, a packet is received only if its error probability can be kept below a predetermined level. Error probability control is achieved by posing a minimum signal to noise ratio (SNR) threshold with corresponding packet internal coding scheme, which upper-bounds the packet data rate. We first consider packet transmission over a single-user wireless fading channel with additive Gaussian noise. We derive the optimal SNR threshold that maximizes the communication throughput. We show under a set of generous conditions that the optimal SNR threshold in the low-SNR regime is proportional to the transmit power; the ratio depends neither on the packet internal coding scheme nor on the pre-determined error probability level. The result is then extended to packet multicasting where common information is transmitted to a group of receivers over fading channels.     

Antenna diversity combining schemes for WCDMA systems in fading multipath channels

In this paper, we analyze the performance of various receive antenna diversity schemes for use in combination with transmit diversity on the downlink of wideband code-division multiple-access third-generation systems. We consider open loop and closed loop versions of both maximal ratio combining and selection diversity, and study the impact of channel correlation on the performance of these schemes. We also present an analysis of the asymptotic performance of coded systems. The analytical results are compared with simulation results obtained in typical channels.     

Rate-distortion optimized unequal loss protection for video transmission over packet erasure channels

Video transmission over networks often suffers from packet loss due to network congestions and stringent end-to-end delay constraints. In this paper, we develop a Rate-Distortion optimized Unequal Loss Protection (RD-ULP) scheme to combat packet loss. Based on packet-level transmission distortion modeling, we estimate the amount of contribution of each video packet to the reconstructed video quality, which defines the priority level of each packet. Unequal amounts of protection are then allocated to different video packets according to their priority levels and the dynamic channel conditions. The proposed RD-ULP resource allocation problem is formulated as a constrained nonlinear optimization problem. An optimization algorithm based on Particle Swarm Optimization (PSO) is then developed to solve the optimal resource allocation problem. Our extensive experimental results demonstrate the effectiveness of the proposed RD-ULP scheme, which outperforms existing methods by up to 2 dB in the reconstructed video quality.     

An enhanced packet scheduling algorithm combined with HARQ for HSDPA system

High speed downlink packet access (HSDPA) is a packet-based data service that supports downlink data rates of up to 14 Mbps in the WCDMA (wideband code division multiple access) system. In HSDPA, the packet scheduler is a key element for high-speed and efficient transmissions. In addition, hybrid automatic request (HARQ) plays a significant role in improving system performance. We propose an enhanced scheduling algorithm combined with HARQ to reduce transfer delay without the degradation of system throughput.     

Linear and non‐linear space diversity combining algorithms over fading channels in TDMA systems

This paper investigates the performances of various adaptive algorithms for space diversity combining in time division multiple access (TDMA) digital cellular mobile radio systems. Two linear adaptive algorithms are investigated, the least mean square (LMS) and the square root Kalman (SRK) algorithm. These algorithms are based on the minimization of the mean‐square error. However, the optimal performance can only be obtained using algorithms satisfying the minimum bit error rate (BER) criterion. This criterion can be satisfied using non‐linear signal processing techniques such as artificial neural networks. An artificial neural network combiner model is developed, based on the recurrent neural network (RNN) structure, trained using the real‐time recurrent learning (RTRL) algorithm. It is shown that, for channels characterized by Rician fading, the artificial neural network combiners based on the RNN structure are able to provide significant improvements in the BER performance in comparison with the linear techniques. In particular, improvements are evident in time‐varying channels dominated by inter‐symbol interference. Copyright © 2001 John Wiley & Sons, Ltd.     

多目标控制系统中TCP粘包问题的解决方法

测控设备采用传输控制协议/网际协议(TCP/IP)作为基础协议,进行遥控多通道并行工作时易造成网络数据粘包.针对此问题,在对TCP协议特点进行分析的基础上,通过讨论TCP编程模型和流交付模型,研究了发生TCP数据流粘包时的网络数据特征,并分析了发生网络粘包的原因,提出了局域网环境下采用短连接、发送端及格式数据组包3种解决网络粘包的方法.实际测试结果证明了这3种方法的适应性及格式数据方法还原TCP网络数据包的有效性,可为基于TCP应用软件开发提供借鉴.     

Frame synchronization for coded systems over AWGN channels

For the additive white Gaussian noise channel, we consider the problem of frame synchronization for coded systems. We present an algorithm that takes advantage of soft information provided by a soft decoder to produce an enhanced estimate of the frame boundary. To reduce complexity, a companion algorithm is introduced that is a hybrid of the optimal uncoded frame synchronizer introduced by Massey and the list synchronizer introduced by Robertson. The high-complexity coded maximum-likelihood frame synchronizer used by Robertson will accordingly be replaced by our algorithm, which operates on decoder-provided soft decisions. The algorithm begins by obtaining a list of high-probability starting positions via the log-likelihood function of the optimal uncoded frame synchronizer. Then, a test /spl delta/ is used to decide if the decision of the optimal uncoded frame synchronizer is sufficient, or whether list synchronization is required. If the test chooses in favor of using the optimal uncoded synchronizer, the estimate is obtained with relative ease. Otherwise, list synchronization is performed, and statistics provided by the decoder are used to resolve the frame boundary. Monte Carlo simulations demonstrate that the frame-synchronization-error rate (the probability of the synchronizer making an error) achieves the lower bound for signal-to-noise ratio values exceeding 1 dB.     

Equal-gain and maximal-ratio combining over nonidentical Weibull fading channels

We study the performance of L-branch equal-gain combining (EGC) and maximal-ratio combining (MRC) receivers operating over nonidentical Weibull-fading channels. Closed-form expressions are derived for the moments of the signal-to-noise ratio (SNR) at the output of the combiner and significant performance criteria, for both independent and correlative fading, such as average output SNR, amount of fading and spectral efficiency at the low power regime, are studied. We also evaluate the outage and the average symbol error probability (ASEP) for several coherent and noncoherent modulation schemes, using a closed-form expression for the moment-generating function (mgf) of the output SNR for MRC receivers and the Pade/spl acute/ approximation to the mgf for EGC receivers. The ASEP of dual-branch EGC and MRC receivers is also obtained in correlative fading. The proposed mathematical analysis is complimented by various numerical results, which point out the effects of fading severity and correlation on the overall system performance. Computer simulations are also performed to verify the validity and the accuracy of the proposed theoretical approach.     

Performance of generalized selection combining over Weibull fading channels

The literature is relatively sparse in performance analysis of diversity combining schemes over Weibull fading channels, despite the fact that the Weibull distribution is often found to be suitably fit for empirical fading channel measurements. In this paper, we capitalize on some interesting results due to Lieblein on the order statistics of Weibull random variables to derive exact closed‐form expressions for the combined average signal‐to‐noise ratio (SNR) as well as amount of fading (AF) at a generalized selection combining (GSC) output over Weibull fading channels. We also use some simple AF‐based mappings between the fading parameters of the Weibull distribution and those of the Nakagami, Rice, and Hoyt distributions to obtain the approximate but accurate average SNR and AF of GSC over these types of channels. The mathematical equations are validated and illustrated by some numerical examples for scenarios of practical interest. Copyright © 2006 John Wiley & Sons, Ltd.     

On the statistics of block errors in bursty channels

In the development of encoding algorithms for image, video, and other mixed media transmissions, it is important to note that the channel “seen” by the applications is the physical channel as modified by the error-correcting mechanisms used at the physical level. Therefore, the statistics of the residual error process is relevant to the design of encoding algorithms. In this paper, we study the second- and third-order statistics of the residual error process when block transmissions are performed over a bursty channel. The effect of interleaving is explicitly studied. The conditions under which a Markovian model for the block errors is adequate are identified. Derivations of the parameters of the block error process are then presented in terms of the parameters of the bit/symbol error process. At higher data speeds an effective interleaving strategy is found to require a very large buffer     

Iterative packet combining schemes for intersymbol interferencechannels

We study packet combining techniques for retransmission schemes over intersymbol interference (ISI) channels. Two types of combining schemes are investigated, namely, maximum-likelihood combining (MLC) and iterative combining (IC). By first employing a precoding technique and then by interpreting the ISI channel as a trellis code, the transmissions of the same data packet at different times through the channel can be treated as the parallel concatenation of recursive trellis codes. If interleavers are used in between retransmissions, "turbo" coding gains can be achieved by iterative equalization. It is shown that IC provides excellent performance and outperforms other forms of combining in terms of frame error rate performance both analytically and through simulations     

Tree algorithms for packet broadcast channels

The multiaccessing of a broadcast communication channel by independent sources is considered. Previous accessing techniques suffer from long message delays, low throughput, and/or congestion instabilities. A new class of high-speed, high-throughput, stable, multiaccessing algorithms is presented. Contentions resolving tree algorithms are introduced, and they are analyzed for specific probabilistic source models. It is shown that these algorithms are stable (in that all moments of delay exist) and are optimal in a certain sense. Furthermore, they have a maximum throughput of 0.430 packets/slut and have good delay properties. It is also shown that, under heavy traffic, the optimally controlled tree algorithm adaptively changes to the conventional time-division multiple access protocol.     

Average SNR of dual selection combining over correlated Nakagami-mfading channels

We investigate the effect of fading correlation and branch gain imbalance on the average output signal-to-noise ratio (SNR) in conjunction with dual selection combining (SC). In particular, starting with the moment generating function of the dual SC output SNR, we derive a closed-form expression for the average output SNR in the general case of correlated unbalanced Nakagami-m fading channels. We then show that the generic result can be further simplified for the special cases of Rayleigh fading, uncorrelated branches, and/or equal average SNRs. Because of their simple form, the given expressions readily allow numerical evaluation for cases of practical interest     

Closed-form analysis of dual-diversity equal-gain combining over Rayleigh fading channels

Starting with a new expression for the probability density function of the signal-to-noise ratio at the output of dual-diversity equal-gain combining (EGC) over Rayleigh channels, we provide closed-form expressions for the average bit and symbol error rate of M-ary phase-shift keying signals. Numerical examples indicate that EGC maintains a good diversity gain as long as the degree of unbalance is not very low but suffers a sharp and significant degradation when the degree of unbalance approaches zero.