An FDD wideband CDMA MAC protocol with minimum-power allocation and GPS-scheduling for wireless wide area multimedia networks

A frequency division duplex (FDD) wideband code division multiple access (CDMA) medium access control (MAC) protocol is developed for wireless wide area multimedia networks. In order to reach the maximum system capacity and guarantee the heterogeneous bit error rates (BERs) of multimedia traffic, a minimum-power allocation algorithm is first derived, where both multicode (MC) and orthogonal variable spreading factor (OVSF) transmissions are assumed. Based on the minimum-power allocation algorithm, a multimedia wideband CDMA generalized processor sharing (GPS) scheduling scheme is proposed. It provides fair queueing to multimedia traffic with different QoS constraints. It also takes into account the limited number of code channels for each user and the variable system capacity due to interference experienced by users in a CDMA network. To control the admission of real-time connections, a connection admission control (CAC) scheme is proposed, in which the effective bandwidth admission region is derived based on the minimum-power allocation algorithm. With the proposed resource management algorithms, the MAC protocol significantly increases system throughput, guarantees BER, and improves QoS metrics of multimedia traffic.     

Multiclass optical orthogonal codes for multiservice optical CDMA networks

Optical code division multiple access (CDMA)-based networks are an interesting alternative to support various traffic types of multimedia applications with highly variable performance targets. Generally, multilength codes are designed to support multirate services, while the multiweight codes are designed to support differentiated quality of service (QoS) for multimedia applications. However, existing optical orthogonal codes (OOCs) are limited to single class or multiclass with restricted weight and length properties. Therefore, there exists a lack of flexibility in the existing OOCs to support arbitrary rate and QoS. This paper presents a proposal of generation procedure and performance analysis of joint multiweight multilength strict OOCs. The approach used in this paper is to apply a methodology strongly relying on developed analytical theory that is supported by computer optimization, because it has turned out that it is mathematically intractable to construct unconstraint joint multilength multiweight OOCs using pure algebraic techniques. The generated code set fulfills the conditions of strictly OOCs, namely, the maximum nonzero shift autocorrelation and the maximum cross correlation constraints of one. The mark position difference (MPD) approach is used to generate in a flexible way the multiclass code set. The MPD results in the simple evaluation of multiclass code set cardinality. Furthermore, the multiple-access interference (MAI) in a multiclass OOC system is evaluated by modeling the interference per class as a Poisson distribution to simplify performance evaluation with acceptable accuracy.     

QoS based fair resource allocation in multi-cell TD/CDMA communication systems

Abstract-In a wireless multimedia code division multiple access (CDMA) system, the resources in terms of transmission rate and power should be efficiently distributed to each user to guarantee its quality-of-service (QoS) requirements. In, this paper, a resource allocation algorithm which combines packet scheduling and power assignment is proposed to achieve efficient resource utilization under QoS constraints. The packet scheduling is based on the fair packet loss sharing (FPLS) principle, and the power assignment is determined by the received power limited (RPL) scheme. The basic idea of FPLS is to schedule the transmission of multimedia packets in such a way that, all the users have a fair share of packet loss according to their QoS requirements, which maximizes the number of the served users with QoS satisfaction. The RPL scheme minimizes the received power for each packet. Given the propagation path loss, it in turn minimizes the transmitted power as well. The intercell interference from the scheduled packets is also limited in order to increase the system capacity.     

Forward-link capacity of a DS/CDMA system with mixed multiratesources

Some studies have been done on capacity of a code division multiple access (CDMA) system with mixed multirate sources. However, a vast majority of these studies have concentrated on the reverse-link. This trend comes from the fact that the capacity of a CDMA system is reverse-link limited. However, the forward-link can be a limiting link because emerging data services are likely to require higher data rates in the forward-link than in the reverse-link. In this paper, we analyze and simulate the forward-link capacity of a CDMA system with mixed multirate sources in a multipath fading channel. The outage probability of the forward-link is derived for a CDMA system with mixed multirate sources. By introducing a forward-link power factor, the forward-link Erlang capacity is obtained in a closed form. The forward-link capacity is analyzed in terms of the number of multipaths, the number of RAKE fingers in a mobile station, closed-loop power control, and impact of soft handoff. The results in this paper can be applied to overall system design of a CDMA system with multimedia services in future mobile communication systems     

Capacity Analysis for Connection Admission Control in Indoor Multimedia CDMA Wireless Communications

In this paper, the capacity analysis for connection admission control is presented for the reverse-link transmission of a packetized indoor multimedia wireless communication system using direct sequence code division multiple access (DS/CDMA). Since CDMA is interference limited, the signal-to-interference-plus-noise ratio criterion is used to check if there is enough system resources (i.e., the CDMA channels and received signal power) for each new connection request. Taking into account the stochastical nature of multimedia traffic, the effective bit rate is used to characterize the resources required by each mobile user and a linear approximation is then used to find the total resources required by all the mobile users already admitted to the system and the new connection request. Transmission errors due to both base station buffer overflow and wireless channel impairments are considered. The capacity of multimedia traffic is determined in such a way that the utilization of the system resources is maximized and, at the same time, the required transmission bit error rate and transmission delay of all users admitted to the system are guaranteed. Computer simulation results are given to demonstrate the performance of the proposed method for capacity analysis.     

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

Three 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 & Sons, Ltd.     

Performance Analysis of Wireless Multimedia DS/CDMA Communications with Power Control and Hybrid ARQ

In this paper, we present aperformance analysis of a wireless multimedia direct-sequence code-divisionmultiple-access(DS/CDMA) system based on different error control schemes and an optimal power control algorithm over multipath Rayleigh fading channels.The error control schemes consist of Forward Error Correction (FEC), diversity, and Automatic Repeat reQuest (ARQ). The concatenated codes with a Reed–Solomon outer code andconvolutional inner code are used as FEC. Since a multimedia system is required to support services with different rates and Quality of Services (QoS), different error control schemes are used to satisfy the requirements of different media. In particular, a power control algorithm which can optimize the capacityperformance of the integrated system is presented. Numerical results will show that power optimization can increase the capacity and decrease the total transmission power. By incorporating diversity and hybrid ARQ along with appropriate code ratesin the optimal power controlled system, dramatic increase in system capacitycan also be achieved.     

Rate-Distortion Optimized Video Transmission Over DS-CDMA Channels with Auxiliary Vector Filter Single-User Multirate Detection

In this paper, we consider the rate-distortion optimized resource allocation for video transmission over multi-rate wireless direct-sequence code-division-multiple-access (DS-CDMA) channels. We consider the performance of transmitting scalable video over a multipath Rayleigh fading channel via a combination of multi-code multirate CDMA and variable sequence length multirate CDMA channel system. At the receiver, despreading is done using adaptive space-time auxiliary-vector (AV) filters. We propose a new interference cancelling design that uses just a single AV filter for single-user mutirate despreading. Our experimental results show that the proposed interference cancelling design has excellent performance in scalable video transmission over DS-CDMA systems that use a combination of multicode multirate and variable processing gain multirate CDMA. The proposed design takes advantage of the fact that single user's video data is transmitted using two spreading codes, one for the base layer and one for the enhancement layers, and of the fact that these spreading codes can have different processing gains. The proposed interference cancelling design is compared with two conventional single-user multirate CDMA receiver configurations, however now we use an AV filter rather than a simple matched filter. We also propose a resource allocation algorithm for the optimal determination of source coding rate, channel coding rate and processing gain for each scalable layer, in order to minimize the expected distortion at the receiver.     

A wireless multimedia CDMA system based on transmission powercontrol

This paper proposes a wireless multimedia code division multiple access (CDMA) system based on transmission power control. When we transmit multimedia information (i.e., speech, image, and data), differences in information rate, traffic performance, and required quality should be taken into account. The wireless CDMA system can achieve a flexible balance if transmission power distribution is controlled by using channel measurement information, i.e., traffic. In this paper, the optimal control of transmission power is derived by linear programming and nonlinear programming. Numerical results using a LAN demonstrate that the proposed method can satisfy the required quality     

Performance analysis of a wireless multirate direct-sequence CDMAusing fast Walsh transform and decorrelating detection

We analyze the performance of a flexible multirate scheme for direct-sequence code division multiple-access (CDMA) mobile radio systems. The proposed scheme uses a variable processing gain serial pseudonoise modulation as a multirate strategy. To reduce the interference effects, the CDMA system utilizes the coherent fast Walsh transform transmission technique. The proposed scheme can be used in the reverse link (mobile-to-base station) of the upcoming third-generation wide-band CDMA system (has the feature of coherent reverse link). We analyze the system performance with and without using a decorrelating multiuser detector. The uncoded bit-error probability (BEP) with and without decorrelating detection on a multipath fading channel is derived analytically. In addition, the validity of the analysis results is demonstrated by computer simulations using the IMT-2000 vehicular multipath channel model. In order to make sure that the proposed processing techniques do not distort the soft values at the demodulator output, the proposed multirate scheme is also simulated in case of using turbo codes. The turbo-coded BEP is calculated for different user data rates and different number of decoding iterations     

Q-learning-based multirate transmission control scheme for RRM in multimedia WCDMA systems

In this paper, a Q-learning-based multirate transmission control (Q-MRTC) scheme for radio resource management in multimedia wide-band code-division multiple access (WCDMA) communication systems is proposed. The multirate transmission control problem is modeled as a Markov decision process where the transmission cost is defined in terms of the quality-of-service (QoS) parameters for enhancing spectrum utilization subject to QoS constraint. We adopt a real-time reinforcement learning algorithm, called Q-learning, to accurately estimate the transmission cost for the MRTC. In the meantime, we successfully employ the feature extraction method and radial basis function network (RBFN) for the Q-function that maps the original state space into a feature vector that represents the resultant interference profile. The state space and memory-storage requirement are then reduced and the convergence property of the Q-learning algorithm is improved. Simulation results show that the Q-MRTC for a multimedia WCDMA system can achieve higher system throughput by an amount of 80% and better users' satisfaction than the interference-based MRTC scheme, while the QoS requirements are guaranteed. Also, compared to the table-lookup method, the storage requirement is reduced by 41%.     

Study on bandwidth control for multiple transmission rates in IEEE 802.11e EDCAF

IEEE 802.11e supports the guaranteed quality of service (QoS) by providing different transmission priorities. IEEE 802.11e improves the media access control layer of IEEE 802.11 to satisfy the different QoS requirements by introducing two channel access functions: the enhanced distributed channel access (EDCA) and the hybrid coordination function (HCF) controlled channel access (HCCA). Signal quality may affect the available bandwidth and transmission rate, because the characteristic of communication channel in wireless environment is in random time‐variation manner. Generally a station using a lower transmission rate will occupy communication channel for a longer time and degrade system performance, which causes unfairness and cannot provide the guaranteed QoS for the stations with higher transmission rates. We propose a bandwidth control scheme (BCS) by combining the IEEE 802.11e enhanced distributed channel access function (EDCAF) protocol to overcome the guaranteed bandwidth issue in multirate environments. A multirate discrete Markov chain model is analyzed for the multirate transmission system in this paper. According to the obtained results, BCS improves performance especially in throughput and makes the different QoS requirements be processed efficiently and flexibly. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance evaluation of multirate DS‐CDMA communication systems with adaptive antennas

Adaptive antennas, with spatial processing, used in code division multiple access (CDMA) systems can enhance range, reliability, and capacity. Moreover, the adaptive beamforming technologies can remove unwanted noise and interference from the received signal. In this paper, we propose the adaptive direct sequence (DS) CDMA antenna receivers and compare their performances in three existing multirate methodologies—variable processing gain (VPG), variable chip rate, and multicode systems for multiuser communications in multipath fading channels. Simulation results show that the processing powers of both narrowband and wideband adaptive antennas are not enough. We propose a powerful processing technique named Wiener Code Filter (WCF) to retrieve the shortcomings. Mean square error (MSE) analyses are also given in this paper. Some simulation examples are given to compare the performances of the proposed multirate structures. Copyright © 2010 John Wiley & Sons, Ltd.     

New concepts and technologies for achieving highly reliable andhigh-capacity multimedia wireless communications systems

The rapid growth of multimedia wireless communications services forces the development of advanced digital wireless systems with high reliability and high speed as well as flexibility for varying traffic conditions. To achieve such advanced wireless systems. New system design concepts different from the conventional ones aiming at increasing system capacity for voice transmission would be required. Since multimedia wireless communications require high quality, high speed, and high flexibility as well as temporary and spatial control of traffic under severe fading environments, the so-called conventional system design concept will be insufficient. New system design concepts and techniques for achieving highly reliable and high-capacity multimedia wireless communications are discussed using both time division multiple access (TDMA) and code division multiple access (CDMA) systems. The demands for high-speed and high-reliability mobile, personal, and multimedia wireless communications services strongly require matching with the trunk network constructed by a broadband optical fiber system or wired system     

Capacity estimation for a multicode CDMA system with SIR-basedpower control

Capacity estimation in code division multiple access (CDMA) systems is an important issue which is closely related to power control. Strength-based power control has been assumed in most analyses in which other cell interference was considered as a known and fixed variable. However, in signal-to-interference ratio (SIR)-based power-control systems, power control and other cell interference are closely related to each other and capacity can be obtained by considering this relationship. This study derives the reverse-link capacity of an SIR-based power-controlled multicode CDMA system supporting heterogeneous CBR and on-off traffic in a multiple cell environment. Mean and variance statistics of total other cell interference, and the effects of traffic and propagation parameters on system capacity are investigated     

Variable-length code construction for incoherent optical CDMA systems

The purpose of this study is to investigate the multirate transmission in fiber-optic code-division multiple-access (CDMA) networks. In this article, we propose a variable-length code construction for any existing optical orthogonal code to implement a multirate optical CDMA system (called as the multirate code system). For comparison, a multirate system where the lower-rate user sends each symbol twice is implemented and is called as the repeat code system. The repetition as an error-detection code in an ARQ scheme in the repeat code system is also investigated. Moreover, a parallel approach for the optical CDMA systems, which is proposed by Marić et al., is also compared with other systems proposed in this study. Theoretical analysis shows that the bit error probability of the proposed multirate code system is smaller than other systems, especially when the number of lower-rate users is large. Moreover, if there is at least one lower-rate user in the system, the multirate code system accommodates more users than other systems when the error probability of system is set below 10⁻⁹.     

On the radio capacity of TDMA and CDMA for broadband wireless packet communications

Studies of the capacity of cellular systems, stated in terms of the admissible number of remote users, have generally been limited to voice telephony. We address the problem of comparing the interference-limited performance of code-division multiple-access (CDMA) and time-division multiple-access (TDMA) systems in a packet-switched environment. The objective is to determine whether the capacity advantages claimed for circuit-switched CDMA still apply in a packet-switched environment, where the natural time diversity of bursty transmission may be a significant factor. Under a set of specific assumptions about the wireless environment (including path loss, shadow fading, multipath delay spread, cochannel interference, power control, and coding), we evaluate the number of users that can be admitted to the system while maintaining some desired quality-of-service (QoS) level. Four different classes of users with different characteristics and requirements are considered. The system capacity is found to depend significantly on the QoS objectives, which might be stated in terms of availability of some specified signal-to-interference level, packet-loss rate, or mean tolerable delay. The main finding is that strict requirements imposed on the radio access level tend to favor CDMA, whereas if some form of packet recovery is allowed at the higher layers (implying a relaxed set of requirements on the radio interface), then a somewhat higher capacity may be achieved by TDMA.     

Comparison of maximum-likelihood-based detection for two multirateaccess schemes for CDMA signals

Future wireless systems will need to accommodate information sources with different data rates. Direct-sequence code-division multiple-access (DS/CDMA) is a multiple access technique that is well suited to provide multirate access. Thus, in this paper, multirate communication systems are considered for the transmission of DS/CDMA wireless signals. Performance for maximum-likelihood-based detection is studied in the context of two multirate access methodologies: multicode access, where high data rate users multiplex their information streams onto multiple codes; and variable spreading length access where signature sequences of different lengths are assigned to users with different data rates. Various maximum-likelihood-based detection schemes for the variable spreading length system are considered as they can achieve near-optimal performance and thus provide reference points for comparison with suboptimal schemes. In addition, asymptotic multiuser performance measures are calculated and bounded to compare performance of the two systems     

Capacity of Multirate Multicell CDMA Wireless Local Loop System with Narrowbeam Antenna and SINR Based Power Control

In this paper, we evaluate the capacity performance of multirate multicell DS-CDMA wireless local loop system with narrowbeam antenna and SINR based power control. Multiple access interference from the surrounding cells in the multicell environment is firstly studied for both uplink and downlink. It can be seen from the results that the capacity can be improved effectively by directional antenna equipped at the subscriber side. More significant improvement can be achieved if multielement antenna array is employed at the base station. In addition, the analysis is also extended to the situation of multimedia multirate transmission. The results show that, regardless of the voice to data user population ratio, the bit rate traffic supported by the system is roughly constant for a set of predetermined parameter values.     

Optical spectral amplitude CDMA communication

We report the first demonstration of bipolar coding techniques in the optical spectral domain for incoherent optical code division multiple access (CDMA) communication. Based on the modulation and detection principles that we have developed, the power spectrum of an erbium-doped superfluorescent fiber source was encoded using bipolar codes and decoded using an optical bipolar correlator. A CDMA testbed consisting of two encoders and one decoder was implemented with bulk optics and free-space transmission. Our measurements verify the correlations between the bipolar codewords and demonstrate the rejection of multiple access interference