Method of link adaptation in enhanced cellular systems to discriminate between high and low variability

Abstract

Method to perform link adaptation at the radio interfaces of an enhanced packet data cellular network handling several Modulation and Coding Schemes (MCS) for maximizing data throughput. In a preliminary off-line step the system behaviour, in terms of net throughput of the various available MCSs, is simulated for different C / l conditions. From the simulation two sets of tables are obtained, each table including upgrade and downgrade thresholds expressed in terms of Block Error Rate (BLER). Thresholds correspond to switching points from an MCs to the two available MCSs having the immediate less or more protection. The two sets of tables are referred to higher or lower diversity RF environments and are further specialized for taking into account EGPRS type II hybrid ARQ, namely Incremental Redundancy (IR). During transmission the transmitted blocks are checked for FEC and the results are sent to the network. The network continuously updates BLER using exponential smoothing. In order to achieve the correct time response, in spite of that RLC blocks can be received or not, a reliability filter is provided whose output is used to decide the weight between the new and old measurements to make the BLER filter impulse response exponentially decreasing with time. The IR efficiency is tested for each incoming block and an indicative variable IR status is filtered using the same approach used for BLER. Each actual threshold of BLER to be used in link adaptation is obtained by a linear interpolation between the tabulated threshold without IR and with perfect IR, both weighed with filtered IR status. Filtered BLER is then compared with said interpolated thresholds for testing the incoming of a MCS switching condition. Power control pursues the goal of maintaining constant QoS peak throughput per time slot(Fig 16).

Description

field of invention [0001] The present invention relates to the field of radiomobile communication systems, and in particular to an improved method for distinguishing between lower variable RF channels and higher variable RF channels with or without incremental redundancy in enhanced cellular mobile systems Link Adaptation Method. Background technique [0002] Background art and related art in the above technical fields are disclosed in the following documents: [0003] International patent application WO 99 / 12304 (ERICSSON (Ericsson)), titled "AMETHOD FOR SELECTING A COMBINATION OFMODULATION AND CHANNEL CODING SCHEMES IN ADIGITAL COMMUNICATION SYSTEMS (a method for selecting a combination of modulation and channel coding schemes in a digital communication system) ". [0004] ·US Patent US 5,764,699 (MOTOROLA Inc. (Motorola)), titled "METHOD AND APPARATUS FOR PROVIDING ADAPTIVE MODULATION IN A RADIO COMMUNICATION SYSTEM (method and device for providing adaptive modulation i...

AI Technical Summary

Problems solved by technology

A first drawback of the method disclosed in the above patent document is that link adaptation is performed without distinguishing between transparent and non-transparent transmission modes, both of which are available for the same modulation scheme, as far as the BLER threshold is concerned. Achieved

The second serious drawback is that the opportunities provided by a single modulation are not fully used, so that the combination with different coding schemes is lacking, since the linking is performed without changing the actual modulation but simply combining it with another coding scheme. When adapting, also force the use of a more troublesome higher modulation

The problem to be solved by link adaptation based on the comparison with the BLER threshold is how to get the actual threshold in the presence of IR for maximizing the data throughput

[0082] At the same time, the method of document WO 00 / 49760 apparently does not suggest any effective solution for the problem of how to compare the variability of the RF channel in the presence of incremental redundancy and link adaptation

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