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Software Defined Radio

Software Defined Radio
Joe Stefanov, David Stewart, Stephan Weiss

In a software defined radio (SDR), functions that were formerly carried out solely in hardware such as the generation of the transmitted signal and the tuning and detection of the received radio signal, are performed by software that controls high-speed signal processors. Because of the ability to be easily reprogrammed, a software defined radio could be programmed easily to operate over a broad range of frequencies, bandwidths and transmission standards.

University of Southampton: 

Wireless Networking

Research topics:

Dynamic channel allocation research  Prof Lajos Hanzo, Dr. Jonathan Blogh
Jon's area of research to date has been the capacity study of GSM based cellular networks, using fixed and dynamic channel llocation schemes. Since the performance of a cellular network is generally limited by the levels of interference present, the effects of using adaptive antenna arrays at the basestations to reduce this interference were analysed.

Work has also been carried out to investigate the network performance benefits of power control and power control used in conjunction with adaptive modulation techniques. It was found that using just power control reduced the required transmission powers, hence extended battery life, whilst simulataneously enhancing the network performance. However, when used with adaptive modulation these benefits were compounded with improved modem throughput.

University of Southampton: 

Multiple Access, Modulation and Transceivers

Research topics:

Multiple-access communications for future wireless systems
Dr. Lie-Liang Yang
With the substantial increase of Internet users and with the development of new services high-speed access in the future generations of wireless systems is an important requirement. Consequently, broadband systems with bandwidths much wider than that of the 3rd-generation systems are required for meeting future requirements. Hence, compatibility with both the emerging Broadband Access Networks (BRAN), which have opted for a multi-carrier, Orthogonal Frequency Division Multiplexing (OFDM) based solution and the existing 2nd- and 3rd-generation CDMA ystems is an important consideration. A potential candidate multiple access scheme meeting these requirements has been proposed by our group. The multiple-access scheme is constituted by frequency-hopping (FH) based multicarrier DS-CDMA (FH/MC DS-CDMA), where the entire bandwidth of future systems can be divided into a number of sub-bands and each sub-band can be assigned a subcarrier. According to the prevalent service requirements, the set of legitimate subcarriers can be distributed in line with the instantaneous information rate requirements. FH techniques are employed for each user, in order to occupy the whole system bandwidth and to efficiently utilize the system's frequency resources. Specifically, slow FH, fast FH or adaptive FH techniques can be utilized depending on the system's design and the state-of-the-art. In FH/MC DS-CDMA systems the sub-bands are not required to be of equal bandwidth. Hence existing 2nd- and 3rd-generation CDMA systems can be supported using one or more subcarriers, consequently simplifying the frequency resource management and efficiently utilizing the entire bandwidth available. This regime can also remove the spectrum segmentation of existing `legacy' systems, while ensuring compatibility with future BRAN and un-licensed systems. Furthermore, a number of sub-channels with variable processing gains can be employed, in order to support various services requiring low- to very high-rate transmissions, for example for wireless Internet access.

University of Southampton: 

Channel Coding

Research topics:

Block and convolutional turbo coding, concatenated coding, space-time coding
Dr. Liew Tong Hooi
Performance of the turbo BCH(63,57) code

Figure 3 : Performance of the turbo BCH(63,57) code for different number of iterations using BPSK over the AWGN channels. The associated Shannon limit of the respective coding rate is also shown.

University of Southampton: 

Multimedia Source Compression

Research topics:

Wideband speech coding for mobile communications
Hee Thong How
Wideband speech coding is of increasing interest today and it is intended for compressing speech or audio signals of 7 kHz bandwidth, sampled at 16 kHz. As shown in Figure \ref{wideband_spectrum}, extending the lower frequency range down to 50 Hz from the 300 Hz lower boundary of narrowband codecs increases naturalness, presence and comfort. At the high end of the spectrum, extending the higher frequency range to 7000 Hz increases intelligibility and makes it easier to differentiate between fricative sounds. This results in an improved speech quality, which will find applications in videoconferencing, loudspeaker telephony and high-definition television.

Typical energy spectrum of a wideband speech signal

University of Southampton: 
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