UE throughput

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  • #7003
    Seerwan
    Participant

    Dear Stefan,

    Hope you are fine.

    To best of my knowledge that the maximum number of parallel streams between the user and the base station depends on the minimum number of antennas e.g. if UE has 2 antennas and the BS has 4 that means there is just two stream between the UE and the BS. however, I have noticed that increasing the number of antennas at (BS) for example to 8 with (transmission mode 4), the throughput of UE is increased as well, so my question what is the reason behind this increase and why? knowingly still the UE with same number of antennas 2 !!.

    Best regards

    Seerwan

    #7007

    Hi,

    you are right the maximum number of spatial streams (transmission layers) is 2 for users with 2 transmit antennas. Therefore the throughput at high SNR (>40dB) should be the same for any number of base station antennas greater or equal to 2. What you will experience however is an SNR gain when more receive antennas at the base station are exploited which originates from receive diversity. This effect is also shown in the documentation (version 1.5) Figure 1.a.

    greetings
    Stefan

    #7010
    Seerwan
    Participant

    Dear Stefan,
    I highly appreciate your help. Stefan please still I am confused from where this increase in TP came if I have just two streams in transmission between sender and receiver, please could you clarify more how the value of throughput increase with increasing the number of antennas at base station while the UE has fix no. of antennas. (note that the mode of transmission that used is mode 4). and where or in which file this happens in the simulator?

    Many thanks Stefan.

    Seerwan

    #7011

    Hi,

    increased throughput in what sense? Do you observe a higher maximum throughput (at very high SNR) ?

    greetings

    #7093
    Seerwan
    Participant

    Dear Stefan,

    May this new year full of health, peace and happiness for you.

    Regarding your question above yes it is but the increase of throughput was with each SNR not just with very high SNR?.

    I know that the throughput is calculated based on the received bits as you said in the last time. But if have just two streams how can the throughput increases?

    Stefan also I wonder why the curve of throughput of cell with increasing the number of antennas at the enodb (at high SNR ) reaches to a saturation value quicker and continue on this value till the end?

    Best wishes

    Seerwan

    #7094

    Hi,

    the throughput saturation value is given by the maximum spectral efficiency, obtained with CQI 15, on two spatial streams (or layers). This saturation value therefore does not change with the number of eNodeB antennas as long as the number of layers is fixed.

    When the number of receive antennas at the eNodeB is increased to a number that is higher than the number of spatial streams, receive diversity comes into play. It means that the received signals are now exploited not only to separate the spatial streams but also to exploit diversity. Due to the feedback algorithm this receive side diversity than translates to an SNR gain. One can say, that due to the use of more antennas at the receiver, the transmission is improved in the sense that a certain CQI is utilized already at lower SNR compared to a situation where there are fewer antennas at the receiver.

    greetings
    Stefan

    #7107
    Seerwan
    Participant

    Dear Stefan,

    Many thanks for your valuable comments and help. Stefan regarding the diversity in the transmission between the UE and enodeB. just I wonder for instance if there is just 1 antenna at the UE and 8 antennas at the enodeB, so in diversity mode how many antennas of the enodeB will be exploited by the UE. in other words, does the UE which has just 1 antenna receives data from (all the antennas) of the enodeB at a time? or there is like an equation or mathematical relation that the enodeB consider it to know how many streams of the same date can be sent over its antenna ports to this UE (e.g. because the UE has just 1 antennas so the enodeB should use for example 2 or 3 to send data instead of using all antennas?

    Kind regards

    Seerwan

    #7245

    Hi,

    I am afraid I don’t fully understand your question. First, in the uplink the UE transmits and the eNodeB receives which is exactly the opposite of your explanation. Second, the number of spatial streams in a MIMO transmission is limited by the minimum number of transmit and receive antennas. This means, as long as you consider an UE with only one antenna, uplink transmission with only one spatial stream (active layer) is possible.

    greetings
    Stefan

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