Advanced Signal Processing for Wireless Multimedia Communications

Article excerpt

Introduction

Potential Applications of Future Wireless Mobile System

The coming generation of wireless communication technology promises a giant leap forward in formation accessibility. Advanced features of wireless mobile systems, including data rates compatible with multimedia applications, global roaming capability, and coordination with other network structures, will enable many emerging applications such as:

* Virtual navigation: The graphical representation of the physical characteristics of an environment, such as streets, buildings, etc., is stored in a remote database. Blocks of this database are transmitted rapidly to a vehicle, where a program renders them so the occupants can visualize the environment ahead.

* Tele-medicine: The paramedic assisting the patient in a remote location must communicate the medical records with the hospital and may need videoconference assistance from a doctor for instructions.

* Crisis management: When severe nature disasters occur and the entire communications infrastructure is in disarray, restoring communications quickly is vital. With wideband wireless mobile ad hoc network, limited and even total communications capability, including internet and video services, could be set up in hours instead of days or even weeks required for restoration of wireline communications.

* Distance learning: Wideband wireless communications will provide cost-effective educational opportunities available on the Internet, for people living in thinly populated or remote areas.

The Role of Signal Processing for Wireless Multimedia Communications

It is anticipated that the future-generation wireless communication systems will incorporate considerable signal-processing intelligence in order to provide advanced services such as multimedia. In order to make optimal use of available bandwidth for these services and to provide maximal flexibility, many such systems will operate as multiple-access systems, in which channel bandwidth is shared by many users on a random-access basis using protocols such as code-division multiple-access (CDMA) signaling. Moreover, in order to support the high data rates inherent in such services, ratios of bit rates to bandwidths will be pushed to their limits. In general, wireless channels can be very hostile media through which to communicate. Physical impairments such as multiple-access interference, co-channel interference, multipath transmission, amplitude fading and dispersion due to limited bandwidth, all contribute to make it difficult to transmit data reliably and quickly through wireless channels. Moreover, the dynamism resulting from user mobility and the above-noted random-access nature of mobile channels, amplify the effects of these impairments, and make them much more difficult to ameliorate. Solution to these difficulties lie in the use of advanced signal processing techniques, and in this paper we present some of the recently developed methodologies for interference rejection that are especially useful for wireless multimedia communications.

Outline of this Article

In particular, we will focus on interference rejection techniques for code-division multiple-access (CDMA) wireless systems. CDMA is the multiple-access scheme adopted in the IS-95 digital cellular standard, and it is the preferred mode of multi-accessing in many current and emerging wireless applications, such as third-generation mobile telephony and wireless personal communications. Our discussion will be primarily focused on the problem of jointly suppressing multiple-access interference (MAI) and intersymbol interference (ISI), which are the limiting sources of interference for high data-rate wireless applications, such as wireless multimedia. After describing the general problem of interference rejection in wireless communications, we present a signal subspace approach to blind joint suppression of MAI and ISI. …