Impact on bit rate - Measuring the Impact of Multiple...

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Measuring the Impact of Multiple Terminal Antennas on the Bit Rate of Mobile Broadband Systems Using Reverberation Chambers Mats Andersson *(1) , Charlie Orlenius (1) , Magnus Franzén (1) (1) Bluetest AB, Götaverksgatan 1, SE-417 55 Gothenburg, Sweden ABSTRACT: The bit rate of new mobile broadband services will be directly affected by the configuration and efficiency of the terminal antennas. Each dB not lost through fading, mismatch and ohmic loss can be used by new (HSDPA and WiMAX) and future (LTE) mobile broadband services for higher user bit rate or use of less spectrum by increasing the modulation rate and/or reducing the coding rate. Fading can be combated using diversity antennas or utilized for higher capacity using partially uncorrelated communication channels created through the use of multiple antennas at both the radio base station and the terminal (MIMO). Low mismatch and low ohmic loss in the antenna and its environment are crucial for high bit rates with terminals using either diversity or MIMO. The only measurement instrument to directly measure the SNR increase of diversity antennas or the increase in capacity of using MIMO antennas is the reverberation chamber. The reverberation chamber simulates a fading environment similar to the one encountered in urban or indoor environments. Measurements in the reverberation chamber are fast and repeatable. The alternative is complex and often unreliable drive tests. Measurements of diversity gain and MIMO capacity in a reverberation chamber are explained and results are presented. INTRODUCTION Broadband connectivity is increasingly going mobile in a similar manner to how telephony went mobile some 20 years ago. The number of mobile users compared to fixed is low to begin with but as coverage and for mobile broadband the bit rate as well is increased more and more users will adopt the new technology. Eventually mobile broadband users will overtake the number of fixed broadband users just as has happened with telephony. However, a big difference with mobile broadband services compared to mobile telephony is that the bit rate in the down and up link will be directly dependent on the available SNR (Signal to Noise Ratio) received at the terminal from the base station and vice versa. In a GSM system the SNR just have to be above a certain threshold value for the service to work. Even if there is 20 dB extra link margin available due e.g. to smart antenna solutions, the bit rate will always be the same 9.6 kbps in the up and down link. Of course, the coverage will be better but that does not affect the majority of users in urban areas but only a few users in rural areas. For the new mobile broadband systems, HSDPA and WIMAX, and in the future LTE (Long Term Evolution) extra SNR can be used in discrete steps to increase the bit rate through higher modulation rates, e.g. going from QPSK to 16 QAM or even 64 QAM, and/or reduced coding. Alternatively the system capacity can be
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This note was uploaded on 05/19/2010 for the course ELECTRICAL ECSE 493 taught by Professor Tholengoc during the Spring '10 term at McGill.

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Impact on bit rate - Measuring the Impact of Multiple...

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