Timeline for OFDM modulator in LTE
Current License: CC BY-SA 3.0
16 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| May 26, 2015 at 2:49 | comment | added | Tyrone | @Naveen Hello Naveen, I was wondering if you can give me your opinion on my other question here. Thanks for everything dsp.stackexchange.com/questions/23648/… | |
| Apr 30, 2015 at 5:52 | comment | added | Serj | @Naveen, in ZF or MMSE we do MIMO channel matrix cancelation so knowing space time coding rule we can simply decode data after such processing. But they are suboptimal, what about ML (e.g. sphere decoding)? Do you know something about this approach application to jointly decoding of Tx Diversity and Spatial MUX? | |
| Apr 30, 2015 at 5:51 | comment | added | Serj | @Tyrone, I mean space time decoder for both Tx Diveristy and Spatial Mux. It is computations greedy algorithm so I think it should be the same decoding for both schemes. | |
| Apr 29, 2015 at 21:35 | comment | added | Naveen | @Serj Sorry, lost tract of this thread. It should be possible to use one Equilizer for both Tx Diversity and Spatial Multiplexing since Equilization is done on layers(between tx and rx layers) after de-precoding(channel matrix multiplied by precoding matrix). I did not find any 3GPP spec which recommends specific equalizers for different transmission modes and channel conditions. I have worked on Matlab LTE systems toolbox where only ZF(for single Ant & TxDiv) and MMSE(SM & CDD) based equalizers are used. My guess it is it is left to the designed to decide on a suitable equalization technique. | |
| Apr 27, 2015 at 15:28 | vote | accept | Tyrone | ||
| Apr 27, 2015 at 15:28 | comment | added | Tyrone | Do you mean to ask, what is the type of decoder used for spatial multiplexing purposed?@Serj | |
| Apr 26, 2015 at 15:33 | comment | added | Serj | I mean spatial-time decoding for MIMO receiver, e.g. MMSE, ML or zero-forcing, no channel FEC decoding. If we use Transmitter Diversity it is some sort of STBC, am I right? While in the case of Spatial Multiplexing it can be V-BLAST or so on. So the question: is one hardware space-time decoder (or we can call it space time equalizer) used for both Transmitter Diversity and Spatial Multiplexing? | |
| Apr 26, 2015 at 14:50 | comment | added | Naveen | @Serj Encoding/Decoding schemes depends on the Channel, it's BER requirement and length of the message to be conveyed. For example Master Information Block(MIB) is a short Broadcast Channel message which carries very important info like Bandwidth, Frame Number, etc. so it is encoded with High redundancy with Tail-biting convolution codes. Shared Channel data on the other hand is much longer and BER requirement are not as stringent. Turbo coding is used for shared channel for increased code rate. So the TM modes do not influence the encoding/decoding scheme. Does this answer your question? | |
| Apr 26, 2015 at 8:34 | comment | added | Serj | @Naveen, thank you for your explanations. I'm wondering, is the same decoding scheme used for the Transmit Diversity and for the Spatial Multiplexing at the reciever side? | |
| Apr 26, 2015 at 4:40 | comment | added | Naveen | @Tyrone Yes, the above example is correct. Same codeword to multiple LAYERS(not antennas) with codeword symbols distributed to the layers in the same manner as in your example for transmit diversity. | |
| Apr 26, 2015 at 1:02 | comment | added | Tyrone | cont.. so for example if we aim for transmit diversity with 4 layers, and we have a codeword: s0s1s3....... sm. Do you send s0 over layer 1 and s2 over layer 2 s3 over layer 3 and s4 over layer 4 and then repeat? | |
| Apr 26, 2015 at 0:48 | comment | added | Tyrone | thank you very much, so in transmit diversity, do you send DIFFERENT QAM symbols constituting the SAME codeword though multiple antenna OR do you send the same ONE symbol over the multiple antennas?@Naveen | |
| Apr 25, 2015 at 21:32 | comment | added | Naveen | cont..The PMI is related to the channel conditions and another UR feedback called Rank Index, but I'm not sure about the exact expression for calculating PMI. | |
| Apr 25, 2015 at 21:31 | comment | added | Naveen | @Tyrone Yes, that is correct. The Transmit Diversity mode serves the purpose of making the transmission more robust my transmitting the same data stream(codeword) through multiple antennae ports. Spatial Multiplexing on the other hand is for increasing throughput, so multiple codewords(here it is 2 since that is the maximum number of allowed codewords) are mapped to multiple antennae ports. Only in case of closed loop spatial multiplexing the precoding matrices are changed based on PMI(Precoding Matrix Indicator) feedback from the UE. | |
| Apr 25, 2015 at 19:13 | comment | added | Tyrone | Thank you @Naveen, for your answer and for the references there in. I have questions regarding layer mapping, is it correct to say, that for transmit diversity there is ONE option available and that is ONE codeword and for spatial multiplexing there is only one option and it is TWO codewords? or can spatial multiplexing have one codeword? Also does precoding the step after the layer mapping, depends on the channel gain conditions? or are they fixed precoding matrices? Thanks | |
| Apr 25, 2015 at 16:27 | history | answered | Naveen | CC BY-SA 3.0 |