Long Term Evolution (LTE) of UMTS Terrestrial Radio Access and Radio Access Network is a Fourth Generation (4G) wireless broadband technology which is capable of delivering high data transmission rates and low latency with reduced costs, among other promises. A key research topic is to design efficient and reliable Physical Downlink Control Channels (PDCCHs) that carry the downlink scheduling assignments and uplink scheduling grants. A number of issues regarding the design and analysis of PDCCHs are discussed in this paper, such as the PDCCH interleaver, power boosting, power lending, receiver handling of power boosting with unknown boosting values, link level performance evaluation, and system level performance evaluation. Based on mathematical analysis and/or simulations, conclusions have been reached, including the adoption of the simple subblock interleaver to achieve desired interference randomization property; power boosting and power boosting limits; and a method of handling power boosting values unknown to the receiver in system simulations. These conclusions have been utilized to develop the LTE standards or adopted in LTE standards.

The paper compares two hybrid automatic repeat request (HARQ) schemes using incremental redundancy (IR) which have been proposed for the UMTS (W-CDMA) high speed downlink shared channel (HS-DSCH). Their relative throughput performance is reported for various channel conditions. It is shown that the two-stage rate-matching scheme has marginally worse performance compared to the alternative block interleaving scheme for certain coding rates and under some channel conditions.

A robust image transmission system incorporating perceptually-based coding and error protection is proposed for wireless channels. The perceptually-based image coder consists of a wavelet transformation, uniform quantization, and variable-length entropy encoding. The coded data is placed in a spatially scalable stream divided into segments of varying perceptual importance and tolerance to transmission errors. A novel unequal error protection system is designed using turbo codes for the wireless channel, neural networks to predict decoder error and calculate erasures, and outer turbo-code concatenation of Reed-Solomon codes at different rates. A model of error tolerance is developed to minimize the added redundancy required to meet the desired throughput performance and visual quality level. The proposed system provides excellent reliability allowing the transmission of high visual quality images at a small additional redundancy and low signal-to-noise ratio (4.5 dB).

It is shown that a neural network can be trained to observe the cross entropy of the outputs of component decoders in a turbo error control system and to accurately predict the presence of errors in the decoded data. The neural network can be used as a trigger for retransmission requests at either the beginning or the conclusion of the decoding process, providing improved reliability and throughput performance at a lower average decoding complexity than turbo decoding with cyclic redundancy check error detection.