What are the MBSFN reference signals for the LTE downlink reference signal and the upstream reference signal?

What are the LTE downlink reference signals and upstream reference signals?

In R9, the downlink defines four reference signals, respectively, for the cell-specific reference signal (C-RS), the user-specific reference signal (UE-RS, also known as Dm-rs), MBSFN reference signal, position reference signal (P-RS).
In R10, the downlink defines five reference signals, namely, the cell-specific reference signal (C-RS), the user-specific reference signal (UE-RS, also known as Dm-rs), the MBSFN reference signal, the position reference signal (P-RS), and the CSI Reference signal (CSI-RS).
Te Uplink uses a single-carrier FDMA technology, and the reference signal and data are multiplexed together using TDM methods. The upstream reference signal is used for the following two purposes.
(1) Uplink channel estimation, used for Enode B-end coherent detection and demodulation, called Drs.
(2) Uplink channel quality measurement, called SRS.

What is the MBSFN reference signal?

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MBSFN (multicast broadcast single Frequency Network)

multicast/Multicast single-frequency network (MBSFN), which requires the simultaneous transmission of identical waveforms from multiple cells. In this way, the UE receiver can treat multiple MBSFN cells as a large cell [1]. In addition, the UE not only will not be affected by the small interval transmission of neighboring cells, but also benefit from the superposition of signals from multiple MBSFN cells. In addition, the advanced UE receiver technology such as G-rake can solve the time difference problem of multipath propagation and eliminate the disturbance in the cell.

The MBSFN is divided into two types: the MBSFN of the dedicated carrier and the MBSFN of the hybrid carrier with the unicast (Unicast), where the hybrid carrier Mbsfnrs design is mainly discussed. Mbsfnrs's design has its special requirements, in a hybrid carrier MBSFN system in a wireless frame, usually most of the resources for the unicast service, and only the individual sub-frames are used for MBSFN business, the typical scenario is to insert an orphaned MBSFN sub-frame within a continuous unicast sub-frame, This makes it impossible for the terminal receiving this MBSFN sub-frame to interpolate channel estimation between the RS of the neighboring subframe as it would when receiving a unicast signal. Therefore, the RS design of the MBSFN must be able to support channel estimation within an orphaned sub-frame.

In addition, because the multi-cell merging greatly increases the number of multipath, so that the frequency selectivity of the MBSFN signal is much larger than the unicast signal, so the need for greater RS frequency domain density. Based on the above considerations, the MBSFNRS structure shown in Figure 5-21 (for 15kHz subcarrier interval) has been adopted after study. Each of the two sub-carriers in the frequency domain is inserted into an RS, and the time domain is inserted into the 1-column pilot for each of the 4 OFDM symbols. It should be stated that the MBSFN uses the extended CP (Extended CP) and a sub-frame contains 12 OFDM symbols when using the 15kHz subcarrier interval. Since 4 types of RS are already defined in Figure 5-20 for the antenna port 0~3 (antenna port 0~3), the T0~T3 signal is shown in the figure, so MBSFN RS is defined as the RS for antenna Port 4 (antenna Port 4) to T4 the signal.
MBSFN Reference Signal Design

MBSFN Reference Signal Design
Unicast RS within a sub-frame which need to be retained is another issue that needs to be discussed. In order to transmit PDCCH, Pcfich, and Phich (up to 4 antenna transmit diversity) in the MBSFN subframe, it is necessary to preserve the 1th and 2nd columns of unicast RS for the demodulation of the PDCCH within the frame. Also, these two-column OFDM symbols must also use the extended CP using the regular CP (other OFDM symbols for the MBSFN subframe).
With this design, the channel estimation of downlink control channel is only one-dimensional interpolation in the frequency domain, which has some influence on the channel estimation performance of PDCCH, and also reduces the range of clock tracking (time Tracking). In the case of time-domain interpolation channel estimation, it is necessary to retain the RS located at the 4th OFDM symbol, and change the RS symbol CP to the conventional CP, which is too much damage to the MBSFN subframe. Therefore, there are proposals that do not even recommend that unicast RS be retained in the MBSFN sub-frame.
However, the complete removal of unicast RS in the MBSFN sub-frame also brings another serious problem, namely, the absence of unicast RS, adjacent cell UE can not be in this sub-frame neighbor measurement. Moreover, because the adjacent cell UE may not know which frame in the cell is MBSFN sub-frame, it causes the UE in any sub-frame that may be MBSFN sub-frame can not be measured in the neighborhood, the performance of the adjacent cell measurement loss is too large.
Thus, the tradeoff is that the 1th and 2nd symbols in the MBSFN sub-frame are used for regular CP, and the unicast pilot is retained for transmission to PDCCH, Pcfich, and Phich channels. Other symbols in the sub-frame are used for MBSFN signal transmission.
In addition to the MBSFN mode of sharing the carrier with unicast signals, another MBSFN mode is the dedicated carrier (DEDICATED-CARRIER,DC) MBSFN, which is suitable for exclusive carrier deployment and does not need to be multiplexed with unicast signals. The LTE DC MBSFN uses 7.5kHz subcarrier intervals, so the symbol length is twice times the 15kHz sub-carrier interval system, so the RS for this configuration MBSFN system needs to be individually designed. After study, the 7.5kHz subcarrier interval DCMBSFNRS structure shown in Figure 5-22 is adopted. As can be seen, considering the change of subcarrier and symbol length, the RS frequency domain density and the time domain density of this structure are basically the same as the 15KHZ structure in Figure 5-21.

What are the MBSFN reference signals for the LTE downlink reference signal and the upstream reference signal?