Adaptive traffic prediction based access control in wireless CDMA systems supporting integrated voice/data/video services

An access control protocol is proposed for integrated voice/data/video code-division multiple-access (CDMA) systems. The protocol involves predicting the residual capacity available for non-real-time data services in reverse link (mobile to base station). Two estimation schemes, a static estimation scheme and a dynamic estimation scheme, are proposed for predicting the residual capacity, the number or the data rate of data packets that could be scheduled at the next time slot. The performances of the proposed estimation schemes are evaluated in view of the outage probability and the mean data message delay.     

Walsh code assignment and data structure for variable data rate communications

In digital communication systems, variable-length Walsh codes, also called orthogonal variable spreading factor codes, are used to support simultaneous variable-rate data transmission. This paper describes algorithms for dynamic variable- length Walsh code assignment. Optimal assignment criterion is derived and an efficient data structure for maintaining variable- length Walsh codes is introduced. The benefits of code reallocation are also studied. Performance is evaluated via simulation.     

Integrating data traffic into a CDMA cellular voice system

Part one of this paper analyzes the effects of data traffic integration into a CDMA cellular voice system. The figure of merit used for the quality of service seen by the voice users is measured by the probability of blocking. The CDMA system under consideration is a power controlled, cellular architecture in which blocking occurs when the total interference level exceeds the background noise level by 10 dB [1]. It is shown that the introduction of data can be done at little or no increase in the probability of blocking on the voice users. In part two we propose and analyze a protocol which achieves the efficient integration of data by maximizing the utilization of the resources and minimizing the delay experienced by the voice users. The proposed protocol admits data traffic into the CDMA cellular system based on the current aggregate voice interference level, and allows for the efficient integration of voice and data without degrading the quality of service for the delay-critical voice traffic. A Markovian model for this protocol is developed, evaluated and compared to computer simulation results.     

Network architecture and traffic transport for integrated wireless communications over enterprise networks

A novel network architecture based on the IEEE 802.6 metropolitan area networks (MAN) is proposed to integrate the wireless and wired segments of a regional enterprise network (REN) within a city. This architecture functions like a distributed switch for all types of services, reducing traffic congestion by sharing the high capacity link dynamically and facilitating signaling, mobility management, call processing and network management through its distributed functions, transport facilities and broadcasting capability. It also serves as a peripheral gathering network of REN traffic for transport over a wide area ATM/BISDN, enabling integration of an enterprise's regional networks into a global EN. Two major wireless applications, i.e., wireless PABX (WPABX) and wireless LAN (WLAN) are discussed to illustrate the advantages of this MAN‐based architecture. Although a REN is likely to support a wide range of different services, voice and data will continue to be the predominant traffic generated by WPABXs and WLANs, respectively, and are also representative of isochronous and asynchronous multimedia traffic carried by future wireless networks. We compare the traffic capacity of several voice transport alternatives under integrated (voice/data) network traffic with various data traffic loads, and study voice and data integration under three different integration schemes by simulations. Results indicate that the MAN‐based architecture is most effective employing queue arbitrated (QA) access for asynchronous traffic, pre‐arbitrated access for constant bit‐rate isochronous traffic, and the new reservation arbitrated (RA) access for variable bit‐rate isochronous traffic, under a scheme that permits full sharing between QA and RA traffic. This revised version was published online in July 2006 with corrections to the Cover Date.     

Theoretical analyses of data communications integrated intocordless voice channels

Dynamic integration of data into voice channels of second-generation cordless systems provides effective channel utilization. This paper proposes and theoretically examines an inhibit and random multiple access (IRMA) protocol for data terminals in an integrated voice and data system by assuming that real-time voice traffic has priority over data. Analytical expressions are derived to quantify the effect of data inhibition on data performance, i.e., throughput and delay for both infinite and finite population models for data terminals. In order to find the possible data throughputs with our channel access scheme for data communication using voice channels while not affecting the voice quality, we investigate the data performance under two extreme situations: 1) no voice load and 2) full voice load. The numerical results indicate that IRMA data performance is comparable to that of slotted ALOHA (S-ALOHA) at lighter loads of less than 0.2 while efficiently sharing the network resources between real-time voice and nonreal-time data traffic. For the data loads above 0.2, IRMA pays a price, but an affordable one, in terms of throughput performance for its ability to accommodate data while assuring quality of voice even when all channels are occupied by voice traffic. An optimum number of terminals and the range of data-transmission probabilities have been deduced as 16 and 0.05-0.15, respectively, in order to achieve maximum throughput with minimum delay while maintaining stable data transmission and voice quality in an integrated system     

Cellular multicode CDMA capacity for integrated (voice and data)services

This paper analyzes the capacity of a multicode direct sequence-code division multiple access (DS-CDMA) cellular architecture supporting integrated (voice and data) traffic. The capacity estimate (on the uplink) is the number of voice users and data users, at different data rates, that the system can support with quality-of-service (QoS) guarantees (frame error rates (FER), outage probability). This estimate is based on an interference analysis that considers both perfect and imperfect power control, different user distributions in the cell, and the coverage trade-off resulting from hand-set power limitations. Localized interference from high speed data (HSD) users, combined with the effects of power control, adversely impacts voice capacity. The analysis investigates the effect of two important factors on capacity: (1) received power levels for the different classes of users and (2) data user activity. The results obtained are useful in designing power allocation and burst-level admission control strategies to optimize the capacity     

Admission policies for integrated voice and data traffic in CDMApacket radio networks

The authors derive optimal admission policies for integrated voice and data traffic in packet radio networks employing code division multiple access (CDMA) with direct-sequence spread spectrum (DS/SS) signaling. The network performance is measured in terms of the average blocking probability of voice calls and the average delay and packet loss probability of data messages. The admission scheme determines the number of newly arrived voice users that are accepted in the network so that the long-term blocking probability of voice calls is minimized. In addition, new data arrivals are rejected if the mean delay or the packet loss probability of data exceeds a desirable prespecified level. A semi-Markov decision process (SMDP) is used to model the system operation. Then, a value iteration algorithm is used to derive the optimal admission control. Two models for the other-user interference of the CDMA system are considered: one based on thresholds and another based on the graceful degradation of the CDMA system performance, and their performance is compared. These admission policies find application in emerging commercial CDMA packet radio networks including cellular networks, personal communication networks, and networks of LEO satellites for global communications     

Selective partial PIC for wireless CDMA communications

This paper deals with a cancellation multiuser detector for CDMA communication systems. The proposed receiver, defined as selective partial parallel interference cancellation (SP‐PIC), is supposed to be used at the end of an up‐link channel characterized by multipath fading phenomena. The SP‐PIC main feature is to perform a weighted selective cancellation of the co‐channel interfering signals according to the received power level. With respect to other approaches, the proposed detector exhibits an improved bit error rate (BER) and a low computational complexity, linear with the number of users. Copyright © 2003 John Wiley & Sons, Ltd.     

Interference-oriented carrier assignment in wireless communications

A carrier assignment problem, suitable for engineering the complex interference conditions of 2.5G and broadband fixed wireless access wireless environments, is addressed. The objective function minimizes the interference levels imposed by the carrier allocation, while the constraints assign the carriers required per cell and prevent unacceptable interference situations. The problem is formally stated and mathematically formulated. Solutions, adhering to the genetic algorithm and the simulated annealing paradigms, are discussed and indicative results are presented.     

Optimal strategies for admitting voice and data traffic in networks of LEO satellites using CDMA

Efficient policies are derived for admitting voice and data traffic into networks of low-earth-orbit (LEO) satellites using code-division multiple-access (CDMA) with direct-sequence spread-spectrum (DS/SS) signaling. The satellites act as bent-pipes; no on-board processing or intersatellite links are present. Dual satellite diversity is used to mitigate the effects of shadowing. The policies assume a movable boundary form, allocate optimally the CDMA capacity (PN codes) to voice and data users, and can increase significantly the number of users served while satisfying their bit error rate (BER) requirements. In contrast to direct admission policies that do not take into consideration the statistical features of the traffic, the new policies do account for the different nature of voice and data traffic and the history of prior transmissions/admissions. Two priority schemes are considered: voice users have higher priority than data users, or voice and data users have the same priority. A modified version of our policies can handle two classes of data users: one with high priority which requires real-time delivery and another with low priority that can be queued; the BER requirements of the two data types may differ. Optimal policies have lower voice blocking rates and data packet error rates than direct admission policies.     

QoS-oriented packet scheduling for wireless multimedia CDMA communications

In the third-generation (and beyond) wireless communication systems, there will be a mixture of different traffic classes, each having its own transmission rate characteristics and quality-of-service (QoS) requirements. In this paper, a QoS-oriented medium access control (MAC) protocol with fair packet loss sharing (FPLS) scheduling is proposed for wireless code-division multiple access (CDMA) communications. The QoS parameters under consideration are the transmission bit error rate (BER), packet loss, and delay requirements. The MAC protocol exploits both time-division and code-division statistical multiplexing. The BER requirements are guaranteed by properly arranging simultaneous packet transmissions and controlling there transmit power levels, whereas the packet loss and delay requirements are guaranteed by proper packet scheduling. 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 under the QoS constraints. Simulation results demonstrate effectiveness of the FPLS scheduler, in comparison with other previously proposed scheduling algorithms.     

A quality-based birth-and-death queueing model for evaluating theperformance of an integrated voice/data CDMA cellular system

Code-division multiple access (CDMA) has been proven to be one of the promising mainstream multiaccessing techniques in future cellular mobile communication systems. A quality-based birth-and-death queueing model is developed for the purpose of evaluating the performance of a CDMA cellular that supports two-rate transmissions. Performance measures obtained include channel utilization and call blocking probability. Based on these results, three call admission schemes are compared     

An adaptive reservation scheme for VBR voice traffic in wireless ATM networks

A reservation scheme, named dynamic hybrid partitioning, is proposed for the Medium Access Control (MAC) protocol of wireless ATM (WATM) networks operating in Time Division Duplex (TDD) mode. The goal is to improve the performance of the real-time Variable Bit Rate (VBR) voice traffic in networks with mixed voice/data traffic. In most proposed MAC protocols for WATM networks, the reservation phase treats all traffic equally, whether delay-sensitive or not. Hence, delay-sensitive VBR traffic sources have to compete for reservation each time they wake up from idle mode. This causes large and variable channel access delays, and increases the delay and delay variation (jitter) experienced by ATM cells of VBR traffic. In the proposed scheme, the reservation phase of the MAC protocol is dynamically divided into a contention-free partition for delay-sensitive idle VBR traffic, and a contention partition for other traffic. Adaptive algorithms dynamically adjust the partition sizes to minimize the channel bandwidth overhead. Simulation results show that the delay performance of delay-sensitive VBR traffic is improved while minimizing the overhead.     

Interaction of TCP and data access control in an integrated voice/data CDMA system

This paper considers the interaction between a proposed data access control scheme and the standardized error recovery schemes on the radio link of a voice/data CDMA system. A data access control scheme for combined voice-data CDMA systems has been proposed and studied in previous literature. The scheme aims to maintain a certain target voice signal to interference ratio (SIR); this is achieved by controlling the data load according to the measured voice SIR. The data users are allowed to transmit in a radio-link time slot with a certain permission probability, which is determined by the base station based on the measured voice SIR in the previous slot. As per the IS-99 standards, however, data transmission operates under the framework of TCP, which is a higher level end-to-end protocol. The TCP data unit, called a segment, is typically equivalent to several tens of physical layer frames; hence, a segment transmission takes up several tens of slots. Due to changes in the number of voice users in talkspurt (which occur on a time scale shorter than a segment transmission time), the slot level data access control scheme can introduce significant variability in the segment transmission time. The effect of such variability on the TCP timers, which operate at the segment level, is of interest. In this paper, an approximate upper bound on the data throughput, taking the presence of TCP into account, is computed. The results provide one with an insight into the interaction of the access control scheme with TCP; they also give practical pointers as to choosing suitable parameters and operating points for the scheme. This revised version was published online in June 2006 with corrections to the Cover Date.     

Access control of data in integrated voice/data CDMA systems:benefits and tradeoffs

In previous work, access control for data has been proposed as a method to ensure adequate quality of service (QoS) in an integrated voice/data CDMA system. The motivation behind access control is to schedule data packet transmissions in slots when voice activity is low and to curtail data transmissions when the voice load is heavy. In this work, the class of probabilistic access control schemes, wherein data transmissions are controlled by dynamically changing the permission probability, are considered. The trigger for changing the permission probability is a measure of the current uplink load. Perfect power control is assumed first, and the trigger for access control is the power control feasibility condition, Schemes based on prediction are analyzed. While prediction schemes are complex to implement, they do provide an upper bound for performance of access control schemes. A simple and practical access control scheme, proposed earlier in the literature, is then extended. It controls the permission probability for data based on uplink load and a 1-bit broadcast feedback to all of the mobiles. The performance of this scheme depends on the choice of three parameters. It is demonstrated that, through a combined choice of these parameters, access control can be tuned to perform as desired and to yield significant capacity gains over not using access control. Results are then extended to the case of imperfect power control, where the outage criterion is based on limiting the total received power at the base station. In this case, too, the simple control scheme is shown to work well     

Performance of cellular packet CDMA in an integrated voice/data network

This paper presents a simulation-based study of cellular packet CDMA systems operating in an integrated voice/data traffic scenario. Spread-spectrum CDMA provides a suitable framework for resource-shared packet transport capable of combining isochronous (voice, ISDN) and bursty data services. In this work, a general network model for cellular packet CDMA with mixed voice/data traffic is described and used to evaluate the capacity/performance impact of several key system parameters. First, the effect of spreading factor (N) and forward error correction (FEC) rate are studied, confirming earlier work indicating a weak dependence onN and a well-defined optimum code rate in the range of 0.5–0.7 (with BCH coding). Next, the effect of propagation loss coefficient () on network capacity is investigated over a range of possible assumptions for, including both constant and distance-dependent models. The results show that system capacity depends strongly on, varying by as much as a factor of 2 over the range of parameters considered. For a given distance-dependent assumption, performance results are also obtained for different cell sizes in order to understand the overall spatial reuse efficiency achievable in different cellular and microcellular scenarios. This is followed by an investigation of traffic source model effects: first the capacity improvement from voice activity detection VAD) is presented, showing the expected 21 gains. Results for varying proportions of voice and data traffic intensities indicate that the operating efficiency does not change significantly as the proportion of bursty data relative to voice is varied.     

Dynamic bandwidth partition schemes for integrated voice,video, and data traffic in the IEEE 802.11e distributed wireless LANs

In mobile cellular networks, bandwidth is deterministic in terms of the number of channels by frequency division, time division, or code division. On the other hand, bandwidth partition schemes in the contention‐based medium access control (MAC) in distributed wireless LANs are extremely challenging due to the contention‐based nature, packet‐based network, and the most important aspect: only one channel available, competed by an unknown number of stations. In this paper, we study this challenging issue. We propose and study four different bandwidth partition schemes for integrated voice/video/data traffic in the IEEE 802.11e wireless LANs: a Static bandwidth Partition (SP) scheme, a Dynamic budget Partition (DP) scheme, a Dynamic bandwidth Partition with Finer‐Tune (DP‐FT) scheme, and a Dynamic bandwidth Partition with Reserved Region (DP‐RR). The proposed schemes are compared and evaluated via extensive simulations. Results show that the DP‐FT scheme is the best scheme. Copyright © 2009 John Wiley & Sons, Ltd.     

An integrated cross-layer study of wireless CDMA sensor networks

In this paper, we characterize analytically the multiaccess interference in wireless code-division multiple-access sensor networks with uniformly random distributed nodes and study the tradeoff between interference and connectivity. To provide a guideline for improving system behavior, three competitive deterministic topologies are evaluated along with the random topology in terms of link-level and network-level (routing) performance. The impact of signature code length and receiver design on the network performance for different topologies is also studied.     

Virtual guard channel for handoff calls in integrated voice/data wireless networks

In this paper, we propose a virtual guard channel (VGC) scheme for handoff calls in integrated voice/data wireless networks. By utilizing the multi-channel capability of data service, the proposed scheme can provide better performance in quality of service (QoS) provisioning and utilize the limited channel resources more efficiently compared with the conventional guard channel (GC) scheme.