Digest 2012-07-12

- The disadvantage (of channel-orthogonality-based VMIMO user pairing) is that it only considers the orthogonality of the MIMO channel matrix itself, while each user’s SNR are not considered. It may occur that the paired users achieve a high data rate for one, and a low data rate for another, for whose channel fading is severe, which is called near-far interference effect, reducing the system channel capacity. [YSong'12] (VM)

Digest 2012-07-11

- Downlink MU-MIMO = SDMA [Li'09CM]

- Uplink MU-MIMO = collaborative spatial multiplexing (C-SM) [Li'09CM]

- UE must be able to decode the data with a BLER below 10 percent. [Liu'12CM]

- PMI and RI jointly represent the spatial directions of the MIMO channel, while CQI indicates the strength of the corresponding spatial directions. [Liu'12CM]

- PMI and/or CQI may be reported either wide-band or on a subband-specific level (the RI is always reported wideband). [Liu'12CM]

- In scenarios where channel reciprocity is valid (e.g., TDD), the UE transmits a specified pilot also known as a sounding reference signal (SRS) based on which the eNB can estimate the channel. Even in this case, CQI feed-back by the UE is necessary to convey the interference conditions at the UE. These can clearly not be inferred from uplink transmissions. [Liu'12CM]

- Opportunistic scheduling: schedule a transmission, at any scheduling instant, to a user with the best channel condition. [Hur'12TSP]

- There are two main methods for Feedback reduction: feedback rate reduction related to quantization, and feedback number reduction related to reducing the number of parameters being fed back. [Hur'12TSP]

- The resource block size is assumed to be known and can be determined at the medium access control (MAC) layer taking into account the number of users in a system. In practice, it is determined by the standard, for example 12 subcarriers in LTE and 24subcarriers in 802.16e. [Hur'12TSP]

- CQI of user- at block- depends on the diversity technique, the noise variance and channel. [Hur'12TSP]