Wednesday, 23 December 2009

Is the LTE Performance Gain Simply Due to Wider Frequency Bands?

There have been various LTE trials going ahead in 2009 and of course the surprise LTE network launch by TeliaSonera who have estimated LTE user data rates to be in the range of 20-80 Mbps. Similar figures have been promoted in other operator trials.

Quite often operators and system vendors refer to the achievable peak rates, ranging from 100 Mbps to as high as 250 Mbps. However, in cases where LTE is deployed in high density, metropolitian areas, these peak data rates are unlikely to be achieved.

Omnitele has just announced that it expects actual data rates to be a lot less than the figues above. Through analysing LTE performance in technical studies and simulations using Omnitele’s state-of-the-art network planning tool analysis on the performance gain of LTE compared to HSPA technology comes mainly from the wider frequency band (up to 20MHz compared to 5 MHz for UMTS). Switching from CDMA to OFDM also has an effect, as does MIMO according to Omnitele. However, significant expectations being put on the performance of MIMO and yet the most critical element of performance which remains under the control of the designer is the antenna, The 3GPP is still proposing how to define requirements for MIMO antennas and it is a pretty complex topic with apparently little consensus developing so far.

Actual LTE user data rates are highly dependent on radio conditions and number of users sharing network resources. Most of the first commercial LTE deployments are said to utilise 20MHz bandwidth and 2x2 MIMO antenna schemes. When breaking down the performance of LTE features in different channel conditions and simulating them in a realistic metropolitan network environment, Omnitele estimated the achievable average LTE user data rates to be in the range of 15-25 Mbps per 20MHz frequency bandwidth.

LTE outperforms the current baseline HSDPA in terms of data rates by a factor of ten and HSPA+ technologies by a factor of 3-4. But it will take more than improved radio performance to really get the best out of LTE.

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