 different OFDM symbols within a slot) multiplexing schemes. As illus- trated in Fig. 4.5, code-division multiplexing between different (per antenna-port) CSI-RS can be performed across frequency by spreading over two adjacent subcarriers (CDM2) to support two antenna ports; across frequency and time by spreading over two adjacent sub- carriers and two adjacent OFDM symbols (CDM4) to enable four antenna ports; across fre- quency and time by spreading over two adjacent subcarriers and four adjacent OFDM symbols (CDM8) to support up to eight antenna port transmission. Combination of code/fre- quency and time-division multiplexing can be used to configure different multiport CSI-RS structures where, in general, an N-port CSI-RS occupies N resource elements within a resource block or a slot. When CSI-RS supports more than two antenna ports, there are mul- tiple CSI-RS patterns/structures based on different combinations of CDM, TDM, and FDM that can be utilized as shown in Table 4.2. The non-zero-power CSI-RS is mathematically represented by sequence rcci-rs(m) which is defined as r'CSI-RS(m) = 2c(2m)] j[1 - 2c(2m+1)]}/v2 where c(i) is a length-31 Gold sequence generated by the pseudo-random sequence generator defined in [6] and initialized with Cinit=[210(N5)mbol -1) nID] mod 231 at the start of each OFDM symbol. In the latter equation, Nslot is the slot number within a radio frame, l is the OFDM symbol number within a slot, and NID is set by the RRC parameter scramblingID or sequenceGenerationConfig [6,13]. If CSI-RS is configured, the CSI-RS sequence r CSI-RS(m) is mapped to resources elements (k,l) such that a(k,l) = where m' = _na] k + a=por2p = when Np = 1 or Np > 1, respec- tively, provided that the resource element (k,l) is within the resource blocks designated to the CSI-RS resource for which the UE is configured. The reference point for k = 0 is subcarrier 0 in common resource block 0. The value of density P and the number of antenna ports are given by RRC parameters [6,13]. The scaling factor BCSI-RS has a 