Variable Spreading Gain Research Articles

Accurate packet error rate analysis of variable spreading gain-code division multiaccess and multicode-code division multiaccess wireless communication networks

This study presents a system-level theoretical analysis of two different types of multirate code division multiaccess (CDMA) wireless communication systems, which include both variable spreading gain (VSG) CDMA and multicode (MCD) CDMA systems. Based on the accurate interference models, the authors derive unified expressions of the cumulative density function of the signal-to-interference-plus-noise ratio in the cases of both binary and quaternary multirate CDMA schemes. This leads us to achieve new packet error rate expressions, which consider the impacts of bit-to-bit error dependence, optimal power transmissions and random users' distributions, for multirate-slotted packet CDMA systems. The expressions are used to investigate the system-level performance of VSG and MCD-based multicellular CDMA networks over Rayleigh fading environment.

Theoretical Analysis on Bit Error Rate of VSG CDMA in Nakagami Fading

In this paper, an efficient analytical technique for bit error rate (BER) of variable spreading gain code division multiple access (VSG CDMA) in Nakagami fading is introduced. Based on the accurate improve Gaussian approximation (IGA) technique, a new BER expression is derived in a closed form. Validated by Monte Carlo simulation, the proposed expression is used to accurately investigate the impacts of channel's conditions, power allocation and random users' distributions on the BER performance.

Adaptive Processing Gain Data Services in Cellular CDMA in Presence of Soft Handoff with Truncated ARQ

An adaptive data transmission scheme based on variable spreading gain (VSG) is studied in cellular CDMA network in presence of soft handoff (HO). The processing gain is varied according to traffic intensity meet-ing a requirement on data bit error rate (BER). The overall performance improvement due to processing gain adaptation and soft HO is evaluated and compared with a fixed rate system. The influence of soft HO pa-rameters on rate adaptation and throughput and delay performance of data is indicated. Further truncated automatic repeat request (T-ARQ) is used in link layer to improve the performance of delay sensitive ser-vices. The joint impact of VSG based transmission in presence of soft handoff at physical layer and T-ARQ at link layer is evaluated. A variable packet size scheme is also studied to meet a constraint on packet loss.

A Linear Programming Approach to Cross-Layer Optimization in Multiclass VSG-CDMA Over Rayleigh Fading

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a new linear programming approach for throughput maximization on the uplink of a multiclass variable spreading gain code-division multiple-access (CDMA) multicellular system in Rayleigh fading for both binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK) modulations. Based on the improved Gaussian approximation technique, we derive exact closed-form expressions of the outage probability, which are used as a physical (PHY) layer constraint of the maximization problem. We show that it is possible to transform the nonlinear constraint into a set of equivalent linear expressions. This facilitates the formulation of a new linear throughput maximization that noticeably requires less computational complexity than the known nonlinear approaches. Furthermore, due to the simplicity of the linear approach, we can include the constraints of such higher layers, i.e., media access control (MAC) and call admission control (CAC) layers, into the proposed formula. Accordingly, we introduce two linear programming optimization formulas. One is for MAC-PHY optimization, and another is for cross-layer optimal CAC policy. In the case of MAC-PHY optimization, the throughput is maximized, at low background noise level, when every user retains the same bit energy, particularly in the case where the difference in data rates is high. Nonetheless, at high levels of background noise, the throughput would be maximized when a larger amount of bit energy is allocated to the high-rate users. For the joint optimal policy, the throughput and the blocking probability are optimized and improved up to 50% in comparison to those of the conventional CAC policy, which is known as the <emphasis emphasistype="boldital">complete sharing</emphasis> policy. </para>

On the comparisons of system performance and capacity of asynchronous STBC MC‐CDMA multirate access schemes

AbstractThree multirate access schemes, multicode, variable spreading gain (VSG), and spectral overlaid multiple‐symbol‐rate (MSR), for asynchronous space‐time block coded (STBC) multicarrier code division multiple access (MC‐CDMA) systems are proposed. The three possible spectral overlaid configurations for MSR systems are also investigated. The expressions to evaluate the multiple access interferences, bit error rate (BER) performances, and system capacities of a antenna STBC MC‐CDMA using the three multirate access schemes are obtained. Transmit power allocation is adjusted according to the service rates and the number of active users in each service class to maintain the link quality and to improve the system capacity. Our numerical results show that systems with multicode access scheme using orthogonal Gold spreading codes and with VSG access scheme have similar system performance and capacity, and both perform in general better than systems with MSR access scheme of any spectrum configurations. In case when non‐orthogonal Gold codes are used, multicode access scheme shows degradation in the system capacity as compared to VSG, due to the presence of larger self‐interference (SI) among the codes used by each user. The achievable capacities for the three spectral overlaid configurations of MSR multirate systems are also compared. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Channel estimation for chip‐level Alamouti coded multi‐rate CDMA: blind subspace algorithms and performance analysis

AbstractIn this work we consider the problem of blind channel estimation for the downlink of a variable spreading gain (VSG) multi‐rate code‐division‐multiple‐access (MR CDMA) system which uses the orthogonal space‐time block coding (STBC) proposed by Alamouti. In contrast to traditional symbol‐level STBC CDMA systems, we consider a chip‐level ST block coding system for which we derive a simple subspace‐based blind channel estimation method. For the derived algorithm we investigate the necessary and sufficient conditions for the channel to be uniquely identifiable up to a complex multiplicative constant. We also analyse the behaviour of the channel estimation algorithm as a function of the data samples utilised, establishing its unbiasedness and providing a closed‐form expression for the mean‐square‐error (MSE) as well as the Cramer—Rao bound (CRB) for the channel estimation performance. Copyright © 2007 John Wiley &amp; Sons, Ltd.

A Linear-Programming Approach for Throughput Maximization of Uplink Multiclass VSG CDMA in Rayleigh Fading

This letter presents a new efficient technique to solve a throughput maximization problem on the uplink of a variable spreading gain code division multiple access (VSG-CDMA) system operated in an independent Rayleigh fading environment. A new linear set of constrains is found that enables a linear-programming solution to the problem of maximizing the overall average throughput in a multiclass system while maintaining the QoS constraints for all users

On the Spectral Efficiency of VSG CDMA in Nakagami and Rician Fading

This paper presents new analytical expressions for the spectral efficiency of variable spreading gain code division multiple access (VSG CDMA) networks in a Nakagami and Rician fading environments. These are used to gain insight into the impact of fading and background noise on the optimal transmit powers. Numerical results for a dual class and 5-class system, reveal that the spectral efficiency is optimized at higher signal-to-noise ratio levels when each user is retaining the same bit energy. However, at lower levels of the signal-to-noise-ratio, the spectral efficiency would be optimized when a larger amount of energy is allocated to the classes of higher data rate, as compared to the lower rate classes

QoS-Aware Distributed Resource Management for a WCDMA Uplink

In this paper, a hybrid resource management system for the uplink in Universal Mobile Telecommunications System wideband code-division multiple access (WCDMA) with components in the Node-B and user equipment (UE) has been proposed. A rate scheduler in the client focuses on average packet delays as a means of abstracting application-specific requirements from the rest of the resource management scheme. It controls uplink transmission through variable spreading gain to optimize resource usage while meeting target delays. Service change requests from the distributed rate schedulers are collectively processed through interservice and intraservice priority queuing in a manner that is shown to exhibit fairness in allocation of resources when cumulative load exceeds system capacity. The performance of the proposed algorithm is explored through discrete-event simulations for three classes of traffic, namely voice, video, and data, over the WCDMA uplink in the presence of short-term Rayleigh fading, automatic repeat request, forward error correction, target transmission delays to meet the respective quality of service, and frame error rate targets in a "multicell" environment. The authors analyze two alternatives for distributed resource management with the UE or Node-B in control of rate scheduling and observe the fairness in resource allocation of both systems. Priority of speech, video, and data traffic is respected and reflected in 95th percentile transmission delays for heavily loaded systems

Cross-Layer optimization for LDPC-coded multirate multiuser systems with QoS constraints

In this paper, we propose a new multirate multiple-access wireless system implemented by variable spreading gain and chip-level random interleaving. The receiver employs a flexible chip-level iterative multiuser detection scheme where the variable spreading gain affects only the despreading parameters. Optimization across the physical and network layers in the uplink of such a system is treated. It is assumed that each user employs an low-density parity-check (LDPC) code to protect its data. At the physical layer, the quality of service (QoS) requirement is specified in terms of the target bit error rate (BER) of each user. Optimal user transmit powers are dynamically adjusted according to the current system load and the corresponding rate requirements. At the network layer, the QoS requirements include the call blocking probabilities, call connection delays, packet congestion probabilities and packet loss rates. To maximize the average revenue of the network subject to both call-level and packet-level QoS constraints, a multicriterion reinforcement learning (MCRL)-based adaptive call admission control (CAC) method is proposed that can easily handle multiple average QoS requirements. Unlike existing model-based approaches, the MCRL-based technique does not require the explicit knowledge of the state transition probabilities to derive the optimal policy. This feature is important when the number of states is so large that model-based optimization algorithms become infeasible, which is typically the case for a large integrated service network supporting a number of different service types

Admission control for variable spreading gain CDMA cellular system with imperfect power control and shadowing

AbstractVariable spreading gain (VSG) CDMA is the prime transmission scheme for supporting multiple services for the next generation cellular systems. As different services have different quality of service and data rate requirements, admission control is essential in safeguarding the performance of different services in VSG‐CDMA cellular systems in harsh wireless environment. In this paper, we propose an admission control scheme for multiple services VSG‐CDMA cellular system in a practical multi‐cell environment where there exist adverse effects due to imperfect power control and shadowing. Rather than with a fixed bound as in previous studies, the admission bound in our scheme is based on the probability distribution of total intra‐cell power (Pin) and other‐cell interference power (Iother). This is used to estimate the blocking probability by utilizing a simple and accurate approximation that incorporates the random nature of Pin and Iother. Evaluation of the impact of power control error to the mean and standard deviation of Pin and Iother, we performed and compared the blocking probability with fixed admission bound scheme in an integrated voice/data environment. Our work has enabled the calculation of the blocking probability and capacity of different mobility users having different power control errors under shadowing. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Design issues of uplink media access control (MAC) protocols for multimedia traffic over DS-CDMA systems

We propose an efficient uplink media access control (MAC) protocol for a variable spreading gain interference-limited wideband CDMA system. It can, with high spectral efficiency, support both real-time traffic like speech and video and also nonreal-time data traffic based on packet transmission. The schemes for power allocation, joint scheduling, and transmission rate adaptation for nonreal time data traffic are designed as integrated parts of the MAC, working together to improve the system performance in terms of capacity and delay. With these associated resource management mechanisms, the performances of the MAC protocol with two different channel-allocation methods for real-time traffic are numerically compared. One is demanding channel allocation, and the other is reserve channel allocation, in which a certain bandwidth is reserved for concurrent real-time traffic.

Dynamic resource scheduling (DRS): a multimedia QoS framework for W‐CDMA

AbstractMulti‐media support is an important feature of third generation (3G) wireless communication systems, and Quality of Service (QoS) is a crucial issue, as in any other networking environment. In this paper, the QoS issues in the wireless last‐mile is investigated for 3G systems based on Wideband‐Code division multiple access (W‐CDMA). Supporting multiple rates in the CDMA environment introduces the power assignment problem, which is coupled with the bandwidth and error QoS parameters. Also, multi‐media traffic flows should be classified and serviced in such a way to provision delay guarantees. In this paper, a new framework, namely dynamic resource scheduling (DRS), is described and extensively studied. In order to serve multi‐media services with different requirements, a family of nine algorithms has been developed within the DRS framework. These algorithms can be categorized with respect to single or prioritized queuing architectures, fixed or variable rate bandwidth and power allocation, and variable spreading gain or multi‐code spreading strategies. The paper presents the performance of the DRS algorithms in comparison with each other and with conventional scheduled‐CDMA (S‐CDMA) and proposed schemes in the W‐CDMA standard. The performance for error and throughput QoS provisioning and power control dynamics are explored; advantages, disadvantages and limitations of the algorithms are discussed. The DRS framework is concluded to be a promising QoS architecture, with a simple, flexible, scalable structure that can be configured according to a given traffic scenario. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Throughput–delay performance of interference level-adaptive transmission in voice∕data integrated CDMA network with variable spreading gain

The throughput and delay performance of adaptive spreading gain uplink packet transmission in real-time and non-real-time data integrated CDMA networks are analysed under AWGN and Rayleigh fading channels. The processing gain for the non-real-time data is adaptively changed according to the total uplink interference level so that a required signal-to-interference ratio (SIR) can be achieved. The optimum values for the required SIR with regard to maximising the throughput are derived as a function of packet length. The optimised adaptive rate system achieves significantly improved throughput compared to the non-adaptive rate system. In addition, the adaptive rate system achieves almost linear increase in packet delay with traffic density, while the packet delay of the non-adaptive rate system shows an abrupt increase as traffic density increases.

Error-rate analysis for multirate DS-CDMA transmission schemes

We analyze and compare the error performance of a dual-rate direct-sequence code-division multiple-access (DS-CDMA) system using multicode (MCD) and variable-spreading gain (VSG) transmission in the uplink. Specifically, we present two sets of results. First, we consider an ideal additive white Gaussian noise channel. We show that the bit-error rate (BER) of VSG users is slightly lower than that of MCD users if the number of low-rate interferers is smaller than a specific threshold. Otherwise, they exhibit similar error performance. Second, we look at multipath fading channels. We show that with diversity RAKE reception, the VSG user suffers from a larger interference power than the MCD user if the channel delay spread is small. The reverse is true for a large delay spread. However, a larger interference power in this case does not necessarily lead to higher error probability. Essentially, our results for both cases show that: 1) in addition to the signal-to-interference ratio (SIR), the difference in error performance between the two systems strongly depends on the distributions of multiple-access and multipath interference; 2) for practical cellular communications, performances for both systems are expected to be similar most of the time.

Optimum rate allocation for two-class services in CDMA smart antenna systems

Transmission bit rates are optimized for two-class traffic in variable spreading gain code-division multiple-access systems with antenna arrays. In an array antenna system, the interference levels experienced by the users belonging to different beams are not the same. Thus, it is not efficient to allocate the same rates to all the data users even though they belong to a cell. Considering this, an optimum rate allocation scheme is proposed for delay-tolerant data users. Additionally, we also propose the optimum rate allocation scheme for voice and data users when a packet scheduling scheme is considered. Numerical results show that, in array antenna systems, the proposed schemes considerably outperform the conventional scheme designed for omniantenna systems.

Multi-phased VSG CDMA with level clipping for high-rate transmission systems

In this letter, a multi-phased CDMA system employing a variable spreading gain (VSG) approach is proposed for high-rate applications, based on four algorithms for selecting a multi-code set. From simulation results, in addition to simple receiver structure thanks to level clipping, the multi-phased VSG CDMA system provides an high bit rate transmission, while maintaining an acceptable performance degradation.

QoS-Based Admission and Load Control Algorithm for Integrated Voice/Data Services over Wideband CDMA

In order to maximize the system capacity in third generation wireless system, efficient call admission and load control algorithms are required to handle the different services having diverse traffic patterns and Quality of Service (QoS) requirements. We propose an admission and load control algorithm that considers the network loading information, propagation conditions, and the interference level. The algorithm takes advantage of the new features of third-generation (3G) wireless system such as the reported pilot measurements, auxiliary pilot for smart antennas, and variable spreading gain. Dynamic resource allocation is employed to scale the amount of the assigned radio resources taking the network loading conditions and channel characteristics into consideration. The results show that integrating the voice service and the data service with high transmission rate (>144 Kbps) can be realized using efficient resource management.

Capacity of a wideband multirate CDMA system with multiservice in the presence of fading and power-control error

The interference-modelling capacity analysis method developed by Gilhousen et al. is modified to make it appropriate for investigating the capacity of a variable spreading gain (VSG) DS-CDMA system with multiservice in the presence of fading (both shadow fading and multipath fading) and power-control error. With this analytical model, the uplink capacity estimate of an integrated voice and long constraint delay data (LCD) services system is obtained. The capacity estimate is the maximum number of concurrent voice users and LCD users that the system can support while their required QoS are met. Further studies are made of the effects of power allocation, power-control error and receiver diversity on system capacity.

MC-VSG BNET system for high-rate wireless personal area network applications

In this paper a multi-coded variable spreading gain (MC-VSG) CDMA system employing a binary transmission of MC signals by introducing a level clipper termed MC-VSG BNet system, is proposed for the candidate of wireless personal area network (WPAN) and 3G cellular applications. With an emphasis on the MC-VSG BNet physical layer we address the concise specification of the MC-VSG BNet system including the spreading code, level clipping, modulation, coding, frame format, and its applications. From the receiver performance based on simulation results, in addition to simple receiver structure, an acceptable performance degradation of the MC-VSG BNet system over the existing DS/CDMA system is observed, while guaranteeing a high bit rate transmission.