Dynamic random access code assignment for prioritized packet data transmission in WCDMA networks

We propose a measurement-based dynamic random access (RA) code assignment procedure for prioritized packet data transmission in wideband code-division multiple access (WCDMA) networks. This dynamic adaptation process is based on analytical performance results derived for random packet access under Rayleigh fading in WCDMA networks. The performance of the proposed measurement-based RA code assignment procedure with three different adaptation methods is evaluated by using computer simulations. The performance of the proposed scheme is compared with those of a retransmission control-based and static channel allocation-based prioritized packet access scheme. An integrated (physical layer and link layer) delay-throughput performance model is presented for finite population RA WCDMA systems. The proposed dynamic RA code assignment procedure can be used in an adaptive quality of service (QoS) framework for dynamically adjusting the QoS of prioritized RA data traffic in the evolving WCDMA-based differentiated services wireless Internet protocol networks.     

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.     

A class of adaptive hybrid ARQ schemes for wireless links

Wireless links are known to suffer location-dependent, time-varying, and bursty errors. This paper considers a class of adaptive error-control schemes in the data link layer for reliable communication over wireless links in which the error-control code and the frame length are chosen adaptively, based on the estimated channel state/condition. Three error-control schemes are considered according to: (1) the number of Reed Solomon code segments a packet is divided into and (2) the way a lost packet is retransmitted. Through throughput performance and computation complexity analyses, these three schemes are compared, and then one of them is claimed to be the most attractive in terms of computation complexity and practicality even though its throughput performance is not the best. The simulation results also verify that this scheme works well over a time-varying fading channel. Error control for the medium access control (MAC) header and its effect on the performance of each error-control scheme are also considered since, without proper error protection for the header, it would be futile to exercise error control on the user data     

A novel random wireless packet multiple access method using CDMA

Random packet CDMA, a novel packet-based multiple access scheme for connectionless, uncoordinated random channel access is proposed. Random packet CDMA, or RP-CDMA, utilizes a novel packet format which consists of a short header and a data portion. Each header is spread with a unique spreading code which is identical for all users and packets, while the data portion of each packet is spread by a randomly chosen spreading sequence. The receiver operates in two stages: header detection and data detection. For header detection a conventional spread spectrum receiver is sufficient. Headers are spread with a large enough processing gain to allow detection even in severe interference. The data portion is decoded with a sophisticated receiver, such as a multiuser detector, which allows for successful decoding of overlapping active packets. It is shown that the RP-CDMA system is detector capability limited and that it can significantly outperform spread ALOHA systems whose performance is limited by the channel collision mechanism. RP-CDMA also experiences a much smaller packet retransmission rate than conventional or spread ALOHA, and provides better spectral efficiencies.     

Performance of H.263 video transmission over wireless channelsusing hybrid ARQ

This paper proposes a hybrid ARQ error control scheme based on the concatenation of a Reed-Solomon (RS) code and a rate compatible punctured convolutional (RCPC) code for low-bit-rate video transmission over wireless channels. The concatenated hybrid ARQ scheme we propose combines the advantages of both type-I and type-II hybrid ARQ schemes. Certain error correction capability is provided in each (re)transmitted packet, and the information can be recovered from each transmission or retransmission alone if the errors are within the error correction capability (similar to type-I hybrid ARQ). The retransmitted packet contains redundancy bits which, when combined with the previous transmission, result in a more powerful RS/convolutional concatenated code to recover information if error correction fails for the individual transmissions (similar to type-II hybrid ARQ). Bit-error rate (BER) or signal-to-noise ratio (SNR) of a radio channel changes over time due to mobile movement and fading. The channel quality at any instant depends on the previous channel conditions. For the accurate analysis of the performance of the hybrid ARQ scheme, we use a multistate Markov chain (MSMC) to model the radio channel at the data packet level. We propose a method to partition the range of the received SNR into a set of states for constructing the model so that the difference between the error rate of the real radio channel and that of the MSMC model is minimized. Based on the model, we analyze the performance of the concatenated hybrid ARQ scheme. The results give valuable insight into the effects of the error protection capability in each packet, the mobile speed, and the number of retransmissions. Finally, the transmission of H.263 coded video over a wireless channel with error protection provided by the concatenated hybrid ARQ scheme is studied by means of simulations     

Adaptive Spatial Filtering for an FH/SSMA Packet Radio Network with Packet Combining

In this paper, packet throughput is analyzed and simulated for a show FH/SSMA packet radio network with adaptive antenna array and packet combining in a Rayleigh fading channel with shadowing. The packet throughput is defined as the average number of captured packets per slot. To enhance the throughput performance, an adaptive spatial filtering through adaptive antenna array and a packet combining scheme are employed. As a random access protocol, slotted ALOHA is considered, and synchronous memoryless hopping patterns are assumed. A packet consists of codewords from an (n, k) RS (Reed-Solomon) code. The tap weights of an adaptive processor is updated by RLS (recursive-least-square) algorithm. From the simulation results, it is shown that a pre-processing by adaptive antenna array and a post-processing by packet combining are very effective to improve reception performance of an FH/SSMA network.     

Design and Analysis of a Channel Access Protocol for WDM-Based Single-Hop Optical Networks*

We propose a channel access protocol for single-hop wavelength division multiplexing (WDM) optical networks. Each node is equipped with a fixed-tuned transmitter, a tunable transmitter, a fixed-tuned receiver, and a tunable receiver. The proposed protocol alleviates the drawbacks of a previous protocol [1], e.g., invalid data transmissions that follows receiver collisions and possible acknowledgment packet collisions with header/data packets, while retaining many advantages. As a result, the network performance in terms of throughput and packet delay is improved. Analytical models based on the timing diagram analysis, the continuous-time Markov chain, and the randomization technique are developed to assess the proposed protocol, and are validated through event-driven simulation. The performance is evaluated in terms of channel utilization, mean packet delay, and packet delay distribution with variations in the number of nodes, the offered traffic, the size of data packets, and the network propagation delay. Through numerical results and simulation studies, we show that the proposed protocol achieves better channel utilization and incurs lower packet delays.     

Modeling TCP SACK performance over wireless channels with semi-reliable ARQ/FEC

Providing reliable data communications over wireless channels is a challenging task because time-varying wireless channel characteristics often lead to bit errors. These errors result in loss of IP packets and, consequently, TCP segments encapsulated into these packets. Since TCP cannot distinguish packet losses due to bit corruption from those due to network congestion, any packet loss caused by wireless channel impairments leads to unnecessary execution of the TCP congestion control algorithms and, hence, sub-optimal performance. Automatic Repeat reQuest (ARQ) and Forward Error Correction (FEC) try to improve communication reliability and reduce packet losses by detecting and recovering corrupted bits. Most analytical models that studied the effect of ARQ and FEC on TCP performance assumed that the ARQ scheme is perfectly persistent (i.e., completely reliable), thus a frame is always successfully transmitted irrespective of the number of transmission attempts it takes. In this paper, we develop an analytical cross-layer model for a TCP connection running over a wireless channel with a semi-reliable ARQ scheme, where the amount of transmission attempts is limited by some number. The model allows to evaluate the joint effect of stochastic properties of the wireless channel characteristics and various implementation-specific parameters on TCP performance, which makes it suitable for performance optimization studies. The input parameters include the bit error rate, the value of the normalized autocorrelation function of bit error observations at lag 1, the strength of the FEC code, the persistency of ARQ, the size of protocol data units at different layers, the raw data rate of the wireless channel, and the bottleneck link buffer size.     

PERFORMANCE OF COMBINED FREE/DEMAND ASSIGNMENT MULTIPLE-ACCESS SCHEMES IN SATELLITE COMMUNICATIONS

By combining free assignment with demand assignment, the combined free/demand assignment multiple-access (CFDAMA) protocol offers a much shorter delay at low and medium traffic loads while maintaining the high channel utility of the demand-assignment multiple-access (DAMA) technique. In these schemes, reservation can be made using pre-assigned (PA) or random-access (RA) request slots, or piggy-backing (PB) the request on a data packet. This paper presents a performance analysis of CFDAMA schemes in packet satellite communications. Illustrative examples are given. They show a good agreement between analytical and simulation results. For low and medium sizes of terminal population, the CFDAMA-PA scheme has an excellent delay-throughput performance. As the terminal population increases, its performance is gradually degraded due to the long waiting time for a request. For a very large number of terminals, the CFDAMA-RA becomes more effective than CFDAMA-PA. This indicates that a CFDAMA scheme using a hybrid PB/RA requesting protocol can provide the best performance for a wide range of terminal population sizes.     

Access scheme for integrated voice/data transmissions over commonpacket channel in 3GPP

In this letter, we propose a flexible channel assignment scheme using preemption as an access method for integrated voice/data transmissions over common packet channel (CPCH) in 3GPP. We analyze the proposed scheme and compare the performance of the proposed scheme with the performance of the basic, channel monitoring, and channel assignment schemes in view of the voice packet dropping probability and the average delay of data packet     

Single tag scheme for segment routing in software-defined network

This paper proposes a scheme to reduce a size of a packet header for a segment routing (SR) scheme in a software-defined network (SDN). The SR scheme inserts a segment identification (SID) list into the packet header to indicate a path for the source–destination pair of the packet. The path can be split into different segments to suit the service requirement and the segments are carried by the SID-list whose length increases with the number of segments. This also increases the packet overhead, and an additional packet is needed if the packet length exceeds the maximum transmission unit (MTU). Moreover, it may not be possible to implement SR in SDN due to the limited number of stacked labels provided by the switch vendor. In the proposed scheme, the SID-list is replaced by a single tag to indicate a node edge, called a swapping node. The tag is replaced by a new tag at the swapping node. With this scheme, the size of SID-list is fixed and does not vary with the number of segments, and no additional packets are required. A mathematic model to balance the number of flow entries in each swapping node is introduced by minimizing the maximum number of flow entries in each swapping node over the network. We implement the proposed scheme on the transmission-Japan science information network (SINET5) and demonstrate confirms its functionality.

     

Multichannel bandwidth allocation in a broadband packet switch

The problem of bandwidth allocation in a packet switch supporting broadband services is addressed. To reduce the performance constraints imposed by limiting a data link to a single broadband packet channel, the author introduces the concept of channel group as a set of broadband packet channels that is viewed as a single data-link connection by routing entities. He uses a two-step bandwidth allocation scheme. At connection setup time, a call is allocated to a channel group. At transmission time, specific channels of a group are optimally allocated to the packets destined to the group. Because of the statistical smoothing of the large number of sources served by a channel group, the traffic performance of the switch is improved. This scheme also allows super-rate switching, i.e., the support of services with peak bandwidth exceeding the capacity of a single packet channel. The author shows the feasibility of this scheme in a Batcher-banyan switch, by implementing in hardware the bandwidth allocation at transmission time. Performance improvements obtained by this scheme are also provided in different traffic environments     

Ordered Packet Length Based Groupwise Transmission Scheme for Rate Scheduling in Burst Switching DS/CDMA System

This paper proposes a new packet rate scheduling scheme for a non-real time data services over the uplink of a burst switching based direct sequence code division multiple access (DS/CDMA) system to support integrated voice/data services. We consider the most general form of optimization problem formulation to determine the optimal number of transmission time groups along with their data rates, which minimizes the average packet transmission delay. An ordered packet length based groupwise transmission (OLGT) scheme is proposed as a simple heuristic solution to this problem, and we present some analytical results for performance comparison with other possible schemes.     

A study of CDPD forward channel performance with coherent and differential detection

The media access control (MAC)-layer performance of the cellular digital packet data (CDPD) forward channel is studied and a new technique to improve the performance is proposed. The study is based on a computer simulation model wherein a CDPD base station continuously transmits a sequence of packets to a CDPD mobile station. We consider a Rayleigh fading channel and demonstrate how the performance metrics are affected by the channel characteristics. At the reception stage, we consider both coherent and differential reception. We argue that the throughput at the MAC layer is affected not only by the error performance of the physical layer, but also by several design characteristics of the MAC layer, including the block length and the alignment between blocks and packets. We illustrate the block error rate, packet error rate, and throughput performance by simulation results, and we show how the receiver may discard data, which is correctly received but nevertheless useless. Our main conclusion is that the CDPD forward-channel performance could be significantly improved should the identified deficiencies are eliminated. For this purpose, we propose a new automatic repeat request (ARQ) protocol that operates in the MAC layer to correct the erroneous blocks by means of retransmissions, and we study its performance. In addition, we discuss an adaptive scheme that maximizes the forward-channel performance by automatically enabling and disabling the ARQ protocol according to the channel conditions.     

An adaptive coding scheme with code combining for mobile radiosystems

The authors propose and study an adaptive error-control coding scheme for binary digital FM (BFM) mobile radio transmission. The scheme employs code combining through packet retransmissions. The number of transmissions of a packet is in proportion to the channel fading/noise levels, which is in contrast to time diversity techniques where a fixed number of repetitions of a data packet is performed even in the absence of channel errors. Furthermore, the receiver uses received signal envelopes as channel state information, which significantly improves the throughput and bit error rate (BER) performance. Performance of the proposed scheme is analyzed for frequency-flat Rayleigh fading channels with additive white Gaussian noise (AWGN), co-channel interference and random FM noise     

Performance evaluation of GSM/GPRS networks with channel re-allocation scheme

Previous work studying the channel allocation schemes in GSM/GPRS network commonly assume that one or two channels are required by a GPRS data for the sake of analytical simplicity. In this letter, we remove the assumption and generalize the GPRS data channel requirement (M channels). Additionally, we propose a channel re-allocation scheme (RAS), executed upon the channel release, by re-allocating the idle channels to the GPRS data which is currently using less than M channels. The example findings show that RAS can significantly decrease the voice call blocking probability and GPRS packet transmission time with slight channel utilization increase and negligible expense on GPRS packet blocking probability. Small M (e.g.M=2) will underestimate the performance achievements of the prior channel allocation scheme as well as RAS.     

Packet data transmission over mobile radio channels

Since in mobile radio Rayleigh fading poses the main threat to accurate data transmission, a mathematical model of the dynamics of Rayleigh fading is used to explore the optimum duration of data packets. The performance criterion is the rate of information transfer through the mobile radio channel. In addition to packet size, the information rate depends on: the speed of the mobile terminal, the channel bit rate, the size of the packet header, and the fade margin of the modulation and coding techniques. In particular, attention is focused on line rates of 16 kb/s and 256 kb/s (which are representative of the rates proposed for digital mobile radio systems in North America and Europe, respectively). At 16 kb/s, the optimum packet size is approximately 17 B (8.5-ms duration). At 256 kb/s, maximum throughput occurs when the packet contains about 48 B (1.5-ms duration). The precise optimum depends on vehicle speed, header size, and fade margin. The optimum packets are considerably shorter than the 125-B packets customarily used in terrestrial and satellite systems     

Channel-aware priority-based groupwise packet scheduling for non-real time data service with burst-switching DS/CDMA system

The algorithm of scheduling scheme of channel-aware priority-based groupwise transmission is investigated for non-real time data service for the uplink direct sequence code division multiple access (DS/CDMA) system using the burst-switching scheme to support the integrated voice/data service. The proposed scheme optimally determines the transmission-time groups and assigns optimal data rates to the users with packets in the transmission-time group depending on priority metric, which involves several parameters such as delay threshold, waiting time, length of packet, and state of the channel, in a way of minimizing the average transmission delay. Simulation results show that the proposed algorithm gives better performance of average transmission delay and packet loss probability than any other conventional algorithms.     

Delay and throughput for three transmission schemes in packet radionetworks

The results of a simulation of a fully connect packet communication network are presented. The network employs the slotted ALOHA channel access protocol, and Reed-Solomon coding is used to correct errors and erasures in the received packets. The network has a fixed number of channels available for packet transmissions. In two of the transmission schemes considered, a given packet transmission occurs on a single channel only. One of these employs fixed assignment of terminals to the channels, and the other employs random assignment. A third method permits each transmitter to hop randomly over the set of channels during the transmission of a packet. The terminal transmits on one channel at a time, and it transmits a fixed number of symbols during each dwell interval. Delay and throughput are evaluated for all three transmission methods. The effects of code rate on the performance of the channel-hopping scheme are explored, and the improvement that can be obtained for the channel-hopping scheme by use of incremental-redundancy transmission is examined     

Design and performance evaluation of an RRA scheme for voice‐data channel access in outdoor microcellular environments

In PCS networks, the multiple access problem is characterized by spatially dispersed mobile source terminals sharing a radio channel connected to a fixed base station. In this paper, we design and evaluate a reservation random access (RRA) scheme that multiplexes voice traffic at the talkspurt level to efficiently integrate voice and data traffic in outdoor microcellular environments. The scheme involves partitioning the time frame into two request intervals (voice and data) and an information interval. Thus, any potential performance degradation caused by voice and data terminals competing for channel access is eliminated. We consider three random access algorithms for the transmission of voice request packets and one for the transmission of data request packets. We formulate an approximate Markov model and present analytical results for the steady state voice packet dropping probability, mean voice access delay and voice throughput. Simulations are used to investigate the steady state voice packet dropping distribution per talkspurt, and to illustrate preliminary voice-data integration considerations. This revised version was published online in June 2006 with corrections to the Cover Date.