Decision feedback equalizer-aided wide-band burst-by-burst adaptive trellis-coded modulation, turbo trellis-coded modulation (TTCM), and bit-interleaved-coded modulation-assisted H.263-based video transceivers are proposed and characterized in performance terms when communicating over the COST 207 typical urban wide-band fading channel. Specifically, four different modulation modes, namely 4QAM, 8PSK, 16QAM, and 64QAM are invoked and protected by the above-mentioned coded modulation schemes. The TTCM assisted scheme was found to provide the best video performance, although at the cost of the highest complexity. A range of lower-complexity arrangements will also be characterized. Finally, in order to confirm these findings in an important practical environment, we have also investigated the adaptive TTCM scheme in the CDMA-based universal mobile telecommunications systems terrestrial radio access (UTRA) scenario and the good performance of adaptive TTCM scheme recorded when communicating over the COST 207 channels was retained in the UTRA environment.

Since wireless channels exhibit dramatic near-instantaneous channel-quality fluctuations, it is unrealistic to expect that a transceiver relying on time-invariant modulation and coding modes is capable of delivering as good a performance as a near-instantaneously adaptive arrangement. Hence, a near-instantaneously adaptive joint-detection code division multiple access (CDMA)-based video transceiver is proposed for wireless video telephony. Specifically, the transceiver is capable of reconfiguring itself in 1, 2 and 4 bits/symbol direct-sequence CDMA modes and delivers an unimpaired video quality associated with a peak signal-to-noise ratio (PSNR) of 34-41 dB for channel SNRs in excess of about 5 dB over the COST207 bad urban channel model at video rates between 5-26.9 kbits/s using 176/spl times/144 pixel quarter common intermediate format (QCIF) and 128/spl times/96 pixel sub-QCIF (SQCIF) video formats.

A range of adaptive orthogonal frequency division multiplex (AOFDM) video systems are proposed for interactive communications over wireless channels. The proposed constant target bit-rate subband-adaptive OFDM modems can provide a lower bit error rate than a corresponding conventional OFDM modem. The slightly more complex switched or time-variant target bit rate AOFDM modems can provide a balanced video quality performance, across a wider range of channel signal-to-noise ratios, maintaining the best video performance. Upon invoking the technique advocated, irrespective of the channel conditions experienced, the transceiver achieves always the best possible video quality by automatically adjusting the achievable bit rate and the associated video quality in order to match the channel quality experienced. This is achieved on a near-instantaneous basis under given propagation conditions in order to cater for the effects of path-loss, fast-fading, slow-fading, dispersion, etc. Furthermore, when the mobile is roaming in a hostile outdoor propagation environment, typically low-order, low-rate modem modes are invoked, while in benign indoor environments predominantly the high-rate, high source-signal representation quality modes are employed.

The performance of turbo-equalized Global System of Mobile Communications/General Packet Radio Service (GSM/GPRS)-like videophone transceivers is studied over dispersive fading channels as a function of the number of turbo equalization iterations. Iteration gains up to 6 dB were attained. The operating channel signal-to-noise ratio (SNR) required for maintaining a peak SNR loss of less than 1 dB was reduced by 3.2 dB for the one-slot system and by 4.1 dB for the four-slot system. The proposed system is capable of providing low-resolution videophone services over GSM/GPRS.

The performance of turbo-equalised GSM/GPRS-like videophone transceivers is studied over dispersive fading channels as a function of the number of turbo-equalisation iterations. Iteration gains in excess of 4 dB were attained. The proposed system is capable of providing low-resolution videophone services over GSM/GPRS.

Multiuser detection assisted, multiple transmit antenna based OFDM arrangements are studied in the context of HIPERLAN 2-like systems. It is demonstrated that the system user capacity can be improved with the aid of unique spatial user signatures, hence supporting a multiplicity of users. The maximum likelihood sequence estimation (MLSE) detection algorithm outperformed the minimum mean square error (MMSE) scheme by about 5 dB in terms of the required signal-to-noise ratio (SNR) and this performance gain manifested itself also in terms of the system improved video performance.

The performance of base station adaptive antenna arrays (AAAs) is investigated in conjunction with fixed channel allocation (FCA) and dynamic channel allocation (DCA) schemes. Locally distributed DCA arrangements are studied and benchmarked against standard FCA, in the context of both line-of-sight (LOS) and multipath propagation environments. One-, two-, four-, and eight-element AAAs are employed using the sample matrix inversion (SMI) beamforming algorithm, in both the up- and the downlink. In most investigated scenarios, the locally optimized least interference algorithm (LOLIA) exhibited the best overall compromise in terms of a set of combined metrics, such as the forced termination probability, new call blocking probability, and the probability of a low quality access.

This article studies the impact of adaptive quadrature amplitude modulation (AQAM) on network performance when applied to a cellular network, using adaptive antennas in conjunction with both fixed channel allocation (FCA) and locally distributed dynamic channel allocation (DCA) schemes. The performance advantages of using adaptive modulation are investigated in terms of the overall network performance, mean transmitted power, and the average network throughput. Adaptive modulation allowed an extra 51% of users to be supported by an FCA 4-QAM network, while in conjunction with DCA, an additional 54% user capacity was attained.

Second-generation (2G) mobile radio standards have not been designed with video communications in mind, although the employment of error-resilient, constant-bit-rate proprietary video codecs over these systems is realistic. The third-generation (3G) systems are capable of providing higher rates and better communications integrity in support of video applications. This paper advocates the employment of burst-by-burst adaptive transceivers, which are capable of accommodating the time-variant channel quality fluctuation of wireless channels. This paper is concluded with a range of performance figures and system design guidelines for wireless systems.

The video performance benefits of burst-by-burst adaptive modulation are studied, employing a higher-order modulation scheme when the channel is favorable, in order to increase the system's bits per symbol capacity and conversely, invoking a more robust lower order modulation scheme when the channel exhibits inferior channel quality. It is shown that due to the proposed adaptive modem mode switching regime, a seamless video quality versus channel quality relationship can be established, resulting in error-free video quality right actress the operating channel signal-to-noise ratio (SNR) range. The main advantage of the proposed burst-by-burst adaptive transceiver technique is that irrespective of the prevailing channel conditions, the transceiver achieves always the best possible source-signal representation quality-such as video, speech, or audio quality-by automatically adjusting the achievable bit rate and the associated multimedia source-signal representation quality in order to match the channel quality experienced. This is achieved on a near-instantaneous basis under given propagation conditions in order to cater for the effects of path loss, fast-fading, slow-fading, dispersion, co-channel interference, etc. Furthermore, when the mobile is roaming in a hostile out-doors-or even hilly terrain-propagation environment, typically low-order low-rate modem modes are invoked, while in benign indoor environments, predominantly the high-rate high source-signal representation quality modes are employed.

The video performance of a 155-Mbps wireless asynchronous transfer mode (WATM) proposal and that of a 2-Mbps Universal Mobile Telecommunications System (UMTS) concept is evaluated for a range of low- to high-quality video application scenarios, various propagation conditions, and video bit rates using the H.263 video codec, assisted by a novel packetization and packet acknowledgment scheme. Orthogonal frequency-division multiplexing is invoked over the highly dispersive channels for conveying high-rate video signals. Various binary Bose-Chaudhuri-Hochquenghem and turbo codes are investigated comparatively, with the conclusion that due to the high error resilience of the video packetization and acknowledgment scheme, the increased power of the higher complexity turbo codec does not translate to substantially improved overall system robustness, although the bit error rate and acknowledgment flag error rate are significantly reduced. The whole range of video resolutions and system parameters is summarized in a number of tables. The required channel signal-to-noise ratio for near-unimpaired video quality is about 16 dB for the inherently lower quality, lower resolution video frame formats, but slightly higher, about 18 dB, for the high-definition formats, where the error-induced subjective video degradations become more objectional over the highly dispersive worst case channels used.

In order to exploit the nonuniformly distributed channel capacity over the cell area, an intelligent 7.3-kB programmable videophone transceiver is proposed, which is capable of exploiting the higher channel capacity of uninterfered, high-channel-quality cell areas, while supporting more robust, but lower bit-rate operation in more interfered areas. The system employed an enhanced H.263-compatible video codec. Since most existing wireless systems exhibit a constant bit-rate, the video codec's bit-rate fluctuation was smoothed by a novel adaptive packetization algorithm, which is capable of supporting automatic repeat request (ARQ)-assisted operation in wireless distributive video transmissions, although in the proposed low-latency interactive videophone transceiver, we refrained from using ARQ. Instead, corrupted packets are dropped by both the local and remote decoders in order to prevent error propagation. The minimum required channel signal-to-interference-plus-noise ratio (SINR) was in the range of 8-28 dB for the various transmission scenarios, while the corresponding video peak-signal-to-noise ratio (PSNR) was in the range of 32-39 dB. The main system features are summarized.

An H.263-based video transceiver is contrived, which maintains a near-constant bitrate and due to the proposed packetisation and packet dropping regime it provides near-unimpaired video quality for frame error rates up to 5%. The target frame error rate is maintained by invoking a novel power-control technique.