Reservation Random Access Protocols Research Articles

An OFDM-aware Reservation Random Access Protocol for Interference Mitigation in OFDMA Femtocells

An efficient random access protocol utilizing the frequency diversity of OFDMA is proposed for mitigating femtocell interference in a decentralized cellular network. The proposed OFDM reservation random access (OFDM-RR) protocol builds upon a generalized version of the frequency-domain backoff scheme, which was originally proposed for WiFi networks. In this protocol, each node chooses one of K subchannels randomly and transmits a short reservation request on the corresponding subchannel. At the end of the slot, the node whose subchannel index is the highest wins the contention and immediately transmits on the full channel. A tie on the highest index is treated as a collision and is resolved by repeating the process with only those nodes involved in the collision. The throughput of this protocol is derived and compared with that of the classic reservation Aloha (R-Aloha) with the same total channel bandwidth. Although channelization increases the transmission time of the reservation packet in OFDM-RR (due to the smaller subchannel bandwidth), the collision resolution mechanism, which reduces the collision rate sharply, helps improve the throughput, particularly in the high-load region. For example, while R-Aloha almost collapses (near zero throughput) at an average load of ten requests/slot, the proposed protocol can provide a throughput of more than 55% at the same load using only two subchannels.

A multiple access protocol with explicit and implicit reservation

AbstractA new version of a MAC‐level protocol is introduced and investigated, operating in a cellular environment, where a base station co‐ordinates mobile users within each cell. The channel multiplexing structure is based on time division, and the slots in each frame are dynamically assigned to the users and their service classes by the cell base station. Decisions are taken on the basis of binary channel feedback information (collision/no collision), by assuming independence in the presence of packets at the mobile stations, and aim at maximizing the one‐step throughput in the current frame. The frame is divided into two periods: the first (short) one contains a number of minislots, equal to the number of ‘real’ slots (i.e. those capable of containing a fixed size packet) of the second part. At the beginning of the frame, the access rights are computed and broadcast to the users; the enabled stations that have a packet to transmit respond, by sending a short burst that contains their ID in a minislot. This most recent feedback is used at the base station to update the parameters of the decision algorithm, which is then re‐applied to yield the final access rights for the second part of the frame. The performance of the scheme is analysed by simulation in the presence of mixed voice and data traffic, and compared with those of a reservation random access protocol using the same algorithm in a single‐phase fashion (RRA‐ISA) and PRMA. Copyright © 2001 John Wiley & Sons, Ltd.

Analysis of frame-based reservation random access protocols for microcellular radio networks

Reservation random access (RRA) protocols have been proposed for handling speech and data traffic on packet wireless networks. An interesting property of some RRA protocols is the capability of decoupling the speech access procedure from the data access procedure, so that speech access performances do not depend on actual data load. Frame-based protocols allow one to get the decoupling property easily. In this paper, we present a Markov model for analyzing the performances of frame-based RRA protocols that operate in a microcellular environment with channel errors. In the paper, this model is used for evaluating the performances of centralized RRA protocols, which use retransmissions for handling channel errors. Both in-slot access schemes, in which all the slots can be used for talkspurt setup and for user information transmission, and out-slot access schemes, with a separate reservation channel, are examined. Moreover, we present and analyze a new, stable, centralized RRA protocol, namely centralized-collision resolution access (C-CRA), which is based on collision resolution techniques.

The RRA-ISA multiple access protocol with and without simple priority schemes for real-time and data traffic in wireless cellular systems

A multiple access protocol, based on a Reservation Random Access (RRA) scheme, is derived for a wireless cellular network carrying real-time and data traffic. Given a TDMA framed channel and a cellular structure, the aim of the protocol is that of maximizing the one-step throughput over an entire frame. This is achieved by deciding on the access rights at the cell base station, which then broadcasts this information at the beginning of the frame. The decision is made on the basis of binary channel feedback information (collision/no collision) over the previous frames, as well as of long term averages of packet generation rates at the mobile stations, assuming independence in the presence of packets at the latter. The resulting protocol has therefore been termed Independent Stations Algorithm (ISA), and the overall scheme RRA-ISA. As in other RRA protocols, time constrained (e.g., voice) traffic operates in a dynamic reservation mode, by contending for a slot in the frame with the first packet of a burst, and then keeping the eventually accessed slot for the duration of the burst; packets of the time constrained traffic unable to access a slot within a maximum delay are dropped from the input buffer. No such constraint is imposed on data traffic. Together with the “basic” version of the access algorithm, three other variants are presented, which exploit three simple different priority schemes in the RRA-ISA “basic” structure, in order to give a prominence to the voice service. The aim of these variants is to improve the performance in terms of the maximum number of stations acceptable in the system, by slightly increasing the data packets delay. All the proposed schemes are analyzed by simulation in the presence of voice and data traffic. Several comparisons show a relevant performance improvement (in terms of data delay and maximum number of voice stations acceptable within a cell) over other protocols that use ALOHA as a reservation mechanism (RRA-ALOHA or PRMA schemes).

A reservation random-access protocol for voice/data integrated spread-spectrum multiple-access systems

Most code-division multiple-access (CDMA) systems described in the literature provide only one single service (voice or data) and employ the strategy of "one-code-for-one-terminal" for code-assignment. This assignment, though simple, fails to efficiently exploit the limited code resource encountered in practical situations. We present a new protocol called reservation-code multiple-access (RCMA), which allows all terminals to share a group of spreading codes on a contention basis and facilitates introducing voice/data integrated services into spread-spectrum systems. The RCMA protocol can be applied to short-range radio networks, and microcell mobile communications, and can be easily extended to wide area networks if the code-reuse technique is employed. In RCMA, a voice terminal can reserve a spreading code to transmit a multipacket talkspurt while a data terminal has to contend for a code for each packet transmission. The voice terminal will drop a long delayed packet while the data terminal just keeps it in the buffer. Therefore, two performance measures used to assess the proposed protocol are the voice packet dropping probability and the data packet average delay. Theoretical performance is derived by means of equilibrium point analysis (EPA) and is examined by extensive computer simulation.

Performance analysis of reservation random access protocols for wireless access networks

A key issue in future wireless access networks is the design of multiaccess protocols that enable dispersed voice and data terminals to efficiently share the terminal-to-base radio channel. A promising class of multiaccess protocols for wireless access is that of reservation random access (RRA) protocols, in which voice talkspurt packets and data packets are statistically multiplexed over TDMA frames. Voice terminals obtain reservations for their talkspurts using a random access protocol. An analysis method for evaluating the performance of a class of RRA protocols is developed. The method is based on a Markovian model, whose stationary solution is obtained via an iterative computational procedure based on matrix decomposition techniques. Subject to a maximum delay constraint, the voice packet dropping rate and distribution of the number of packets dropped from a talkspurt are evaluated for three RRA protocol examples, and comparisons are made with the performance of an ideal hypothetical multiplexer. The transient performance of RRA protocols is evaluated by simulating their response to sudden changes in the number of active voice terminals. Finally, suggestions for the design of integrated voice/data RRA protocols are made. >

On the voice‐data integration in third generation wireless access communication networks

AbstractMobile wireless communications, which includes cellular telephones, land mobile radio, and personal communication systems, have experienced enormous growth over the last decade. Data services represent a critical component of future wireless communications, but have received little attention. While some attention has been given to specialized mobile data networks, less has been directed at the ongoing design of data services in evolving digital cellular networks. In this paper we report on the results of a simulation study which explores voice‐data integration performance in third generation wireless communication networks. These networks are designed to provide access to broadband ISDN networks for large numbers of mobile voice and data users. The primary goal of the paper is the development of multiple access transmission protocols that will enable the voice and data terminals to efficiently share the terminal to base station wireless channel. Reservation Random Access (RRA) protocols are used for voice traffic, and multiple random access contention protocols are used for data traffic. The RRA protocols used enable the data terminals to precisely determine the end of voice packet contention periods, therefore providing a natural separation between voice and data contention. Such voice data integration mechanisms allow the voice contending terminals to resolve their contention without any interference from the data terminals. Data contention resolution does not degrade the voice performance, since it follows the voice contention resolution. The above approach is a promising alternative to other existing proposals due to its superior data packet throughput‐delay performance under steady state, and voice performance under transient conditions. Our results show that dispersed voice and data terminals can efficiently share a wireless channel.