Medium Access Control Protocols for Multimedia Traffic in Wireless Networks

This article presents a survey on medium access control protocols for multimedia t raf f ic in wireless networks. A basic overv iew o f MAC pro toco l concepts i s presented, a n d a f r a m e w o r k i s d e v e l o p e d o n w h i c h to base qua l i t a t i ve comparisons. The M A C protocols covered in this article include third-generation TDMA and CDMA schemes intended for use in a single-hop wireless system. The operation of each protocol i s explained, and its advantages and disadvantages are presented. Finally, a qualitative comparative outline of the discussed protocols is provided, based on multimedia traffic requirements. ne of the driving forces of the next generation of wireless communication and computing networks is the promise of high-speed multimedia services. Third-generation systems, such as the International Mobile Telecommunication System (IMT-2000) network (formerly known as the Future Public Land Mobile Telecommunication System, FPLMTS) and the Universal Mobile Telecommunication System (UMTS), promise to provide multimedia services to mobile and fixed users via wireless access to the global telecommunications infrastructure [l, 21. The IMT-2000 is a universal, multifunction, globally compatible digital mobile radio system that plans to integrate all traffic types and all wireless systems under a common set of formats. The standards for IMT-2000 are being developed by the International Telecommunication Union (ITU) standards organization for global communications [l]. UMTS is a similar global wireless solution, and is being standardized by the European Telecommunications Standards Institute (ETSI) [2]. Among the requirements for third-generation systems is the ability to support multimedia traffic. The various classes of traffic can be distinguished as suggested by the Asynchronous Transfer Mode (ATM) Forum [3]: Constant bit rate (CBR) traffic (digital voice and video) Real-time variable bit rate (rt-VBR) traffic (compressed Non-real-time variable bit rate (nrt-VBR) traffic (data) voice and video) The work of Ian F. Alqyildiz and Janise McNair is supported by Department of Defense undergrant number MDA 904-97-C-1105-0003. The work of Loren Cawasco Martorell is supported by the Comisio’n Inteministerial de Ciencia y Tecnologi’a under Grant (TIC 98-0263), Spain, and the Comunitat Aut’onoma de les Illes Balears, Spain. Available bit rate (ABR) traffic (non-time-critical data) Unspecified bit rate (UBR) traffic (file transfer, system backup, e-mail) In a wireless system consisting of a number of mobile terminals that transmit traffic of any type on a shared medium to a centralized base station, a procedure must be invoked to distribute packet transmission among all users. This procedure is known as a medium access control (MAC) protocol. MAC protocols are often classified according to their method of resource sharing, as well as their multiple access technology [4]. The resource sharing methods include dedicated assignment, random access, and demand-based assignment. Dedicated channels assign each user a predetermined and fixed allocation of resources, regardless of the user’s need to transmit. Dedicated assignment schemes are appropriate for continuous traffic, but can be wasteful for bursty traffic. On the other hand, random access channels allow all users to contend for the channel by transmitting as soon as packets are available to send. Random access is suitable for bursty data traffic, but is not desirable for delay-sensitive traffic. Demand-based assignment schemes assign resources according to requests, or reservations, submitted by users. Once the requests are transmitted (using either dedicated or random access channels) and processed, users can be assigned resources according to the results. Demand-based channels are useful for variablerate traffic and the hybrid conditions of multimedia traffic. However, the additional overhead and delay caused by the reservation process can degrade performance. In addition to the resource sharing method, the multiple (or multi) access scheme of a MAC protocol establishes a method of dividing the resources into accessible sections. Three accepted methods for resource division are frequency-division multiple access (FDMA), time-division multiple access IEEE Network JulyiAugust 1999 0890-8044/99/$10,00