Abstract
For the well-known 3G mobile communications standard UMTS, four different service classes have been specified. Considering two turbo decoding algorithms, like SOVA and log-MAP, it would be desirable to use an efficient turbo decoder. In this paper this decoder is shown to adapt dynamically to different service scenarios, considering parameters like performance and complexity for indoor/low range outdoor operating en-vironment. The scenarios show that for streaming service class real-time class applications the proposed de-coding algorithm depends on data rate; for the majority of scenarios SOVA is proposed, whereas log-MAP is optimal for increased data rates and medium-sized frames. On the other hand, conversational service class real-time applications cannot be established. For the majority of non real-time applications (interactive and background service classes) either algorithm can be used, while log-MAP is proposed for medium data rates and frame lengths.
Highlights
Introduction and Universal Mobile Telecommunications System (UMTS) Data FlowChannel coding is a critical signal processing element in modern mobile communications systems
The scenarios show that for streaming service class real-time class applications the proposed decoding algorithm depends on data rate; for the majority of scenarios soft output Viterbi algorithm (SOVA) is proposed, whereas log-MAP is optimal for increased data rates and medium-sized frames
Soft-input/soft-output (SISO) decoder is part of a turbo decoder and two candidate algorithms to be used in a SISO decoder are soft output Viterbi algorithm (SOVA) and log maximum a-posteriori algorithm [2,5,6,7]
Summary
Channel coding is a critical signal processing element in modern mobile communications systems. Turbo codes have been incorporated as a channel coding scheme in UMTS for data rates higher or equal to 28.8 kbps [2] They provide high coding gains in flat fading channels with the use of outer block interleaving [3,4]. According to UMTS specifications, a transport channel transfers data over radio interface from Medium Access Control sublayer of layer 2 to physical layer and is characterized by its transport format set, which consists of different transport formats. They must have the same type of channel coding and time transmission interval (TTI), while the transport block set or data frame size can vary. The maximum acceptable delay for conversational class is 80 msec, for streaming it is 250 msec, for interactive it is 1 sec, while for background it is higher than 10 sec [2,11]
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