Enhanced Radio Access Technologies for Next Generation Mobile Communication phần 9 pot

EVOLVED UTRA TECHNOLOGIES 229

domain compared to the reference symbols of the first OFDM symbol. It was

reported that by multiplexing reference signals into two OFDM symbols within

a sub-frame, low-to-high mobility environments up to, e.g., 350 km/h can be

supported without additional reference signals in the time domain.

4.1.2 Orthogonal reference signals

In E-UTRA, it should be possible to provide orthogonal reference signals between

cells of the same Node B as well as between different transmit antennas of the same

cell. Orthogonal reference signals between transmit antennas within the same cell

is e.g. needed to support downlink transmit diversity and MIMO transmission.

(1) Orthogonal reference signals for different transmission antennas

Orthogonal reference signals for different transmit antennas of the same cell/beam is

established by means of FDM, possibly in combination with TDM. Thus, reference￾signal multiplexing with different antenna-specific frequency (or time) shifts is used

for each antenna. The main reason for relying on FDM/TDM-based orthogonality

between transmit antennas of the same cell/beam is that it provides more accurate

orthogonality compared to CDM-based orthogonality since no inter-code inter￾ference occurs in a frequency-selective fading channel. A high level of orthogonal

accuracy is necessary to separate composite streams from different antennas in

MIMO multiplexing and MIMO diversity schemes.

(2) Orthogonal reference signals for different cells in the same Node B

CDM-based reference-signal orthogonality is used between different cells/beams

belonging to the same Node B in order to suppress the mutual interference particu￾larly near the cell boundary. The merit of CDM-based orthogonality, compared to

FDM-based orthogonality, between cells of the same Node B is a better tracking

ability for the channel estimation, particularly UEs far from sector borders, since the

density of the CDM-based orthogonal reference symbols in the frequency domain

is higher than in case of FDM-based orthogonality.

Figure 6 shows the principle of the intra-Node B orthogonal reference signal

employing the combination of a Node B-specific scrambling code and cell-specific

orthogonal sequence in the same Node B. As shown in Figure 6, we employ the

same scrambled code among all cells belonging to the same Node B unlike in

the WCDMA scrambled code assignment. Furthermore, a cell-specific orthogonal

sequence is applied in order to distinguish cells (typically three or six) within

the same Node B. Therefore, the resultant cell-specific scrambled code for the

reference signal, pnm (n is the cell belonging to the same Node B and mis the index

for the reference symbols), is generated through the combination, i.e., multipli￾cation, of a Node B-specific scrambled code and cell-specific orthogonal sequence

represented as

(2) pnm = cm ·snm mod SF 

In this equation, cm denotes the Node B-specific scrambled code, and snm is the

orthogonal sequence with the spreading factor of SF employed in the n-th cell.

230 CHAPTER 7

Node B-specific

scrambling code

Sector-specific

orthogonal

sequence

Sector #1

Sector #2

Sector #3

Mutually orthogonal sequence

Spreading factor

Frequency

c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12

s1,1 s1,2 s1,3

s2,1 s2,2 s2,3

s3,1 s3,2 s3,3

s1,1 s1,2 s1,3

s2,1 s2,2 s2,3

s3,1 s3,2 s3,3

s1,1 s1,2 s1,3

s2,1 s2,2 s2,3

s3,1 s3,2 s3,3

s1,1 s1,2 s1,3

s2,1 s2,2 s2,3

s3,1 s3,2 s3,3

Figure 6. Principle of intra-Node B orthogonal reference signal structure

The cell-specific orthogonal sequence is generated by a Walsh-Hadamard sequence

or phase rotation sequence. Here, we assume a cell-specific orthogonal sequence

generated by phase rotation as indicated in the following equation assuming

Nsectors (SF = N in the same Node B.

(3) snm = exp

j

2n

N m



Thus, in the three-cell configuration at each Node B, the phase rotation of 0, 2/3,

and 4/3 is added to Sectored beams 1, 2, and 3, respectively. Using the orthogonal

reference signal in Figure 6, intra-Node B orthogonality in the channel estimate is

achieved by despreading CDM based reference symbols in the frequency or time

domain. Note that the channel estimate at each sub-carrier is directly used without

despreading for the UE without intra-Node B macro-diversity.

4.2 Broadcast Channel (BCH)

The broadcast channel (BCH) is used to broadcast system and cell-specific control

information over the entire cell area. The broadcast control information includes

information related to connection setup, cell selection, and re-selection, etc..

4.2.1 Broadcast Control Information

Broadcast control information can be categorized into cell-specific information,

Node B-specific information, and system-specific information. Furthermore, another

level of categorization is primary information, which is necessary to be immediately

available to UE after cell search and initial acquisition, and non-primary information.

Table 2 lists different kinds of broadcast control information together with the

categorization according to above.