4 ms·

Very good post, thank you for taking time to write this. One correction: radios are not SDRs. They are ASICs (and occasionally FPGAs) with all the signal proces

Very good post, thank you for taking time to write this. One correction: radios are not SDRs. They are ASICs (and occasionally FPGAs) with all the signal processing done in dedicated hardware. The software merely configures and controls this process. The ASIC is designed to be hardware-ready to support several technologies (WCDMA/GSM/LTE/5G), via later software upgrade as you mention.

zw123456 7y ago
It is not exactly SDR's but getting further into the weeds here, the radio is split into two parts, this actually started with the introduction of LTE. The BBU (Baseband Unit) is centrally located or can be collocated and the RRU (Remote Radio Head) is essentially the PA/LNA radio chain (Power Amp, i.e. transmitter and the Low Noise Amp, receiver) and some other things. The connection between the two is CPRI which carries the I&Q (Phase and Amplitude) information, basically the modulation scheme is QAM. So the BBU's are generally somewhat programable but it depends on the exact type manufacturer. For 5G the BBU function will actually run in a VM instance on a server stack. The RRU is sort of "dumb". So for 5G I would say it is pretty much an SDR but depending on the vintage of 4GLTE it may or may not be. Older BBU's are not re-programmable but many of the newer ones were designed to allow an upgrade to 5G, when they were made it was anticipated that the standards would firm up and then new firmware could be uploaded into them.
- jmiskovic 7y ago
  To my best understanding, the BBU also uses ASIC to construct modulated symbols for RU. The necessary data throughput combined with low latency and time-critical operation while keeping low power consumption is simply not achievable in SW. As one mmWave example, the BBU has to keep track of current spatial position of UE and update the beam steering information to track UEs in motion. Most of these decisions have timings expressed at 1e-7 seconds order of magnitude, while SW used can react with 10ms precision. I would be interested in any info that shows SDR being used as part of radio.

zw123456 7y ago

It is not exactly SDR's but getting further into the weeds here, the radio is split into two parts, this actually started with the introduction of LTE. The BBU (Baseband Unit) is centrally located or can be collocated and the RRU (Remote Radio Head) is essentially the PA/LNA radio chain (Power Amp, i.e. transmitter and the Low Noise Amp, receiver) and some other things. The connection between the two is CPRI which carries the I&Q (Phase and Amplitude) information, basically the modulation scheme is QAM. So the BBU's are generally somewhat programable but it depends on the exact type manufacturer. For 5G the BBU function will actually run in a VM instance on a server stack. The RRU is sort of "dumb". So for 5G I would say it is pretty much an SDR but depending on the vintage of 4GLTE it may or may not be. Older BBU's are not re-programmable but many of the newer ones were designed to allow an upgrade to 5G, when they were made it was anticipated that the standards would firm up and then new firmware could be uploaded into them.

jmiskovic 7y ago
To my best understanding, the BBU also uses ASIC to construct modulated symbols for RU. The necessary data throughput combined with low latency and time-critical operation while keeping low power consumption is simply not achievable in SW. As one mmWave example, the BBU has to keep track of current spatial position of UE and update the beam steering information to track UEs in motion. Most of these decisions have timings expressed at 1e-7 seconds order of magnitude, while SW used can react with 10ms precision. I would be interested in any info that shows SDR being used as part of radio.