# Low-Computational Extended Orthogonal Matched Filter Structure for Multiuser Detection
## 4 Performance Evaluation and Discussion
### Results and Discussion
#### 4.2.2 Cqet  
The parameters of CQET are shown in Table 4. \"Other users\" in the table means desired users other than desired user 1 and the interfering users. The transmission power of desired user 1 is set to 1, and the transmission power of other users is set randomly according to DIR. Here, DIR is set to \(-50\) dB to \(0\) dB in \(5\) dB steps. The total number of users in a network, including desired user 1, other desired users, and interfering users, is set to eight or 30. That is, the former is the case in which the total number of users is within the number of antenna elements, and the latter is the case in which the total number of users exceeds the number of antenna elements and the array antenna characteristics deteriorate. In addition, the number of desired users is one, two and half of the total number of users. When the number of desired users is one, the characteristics of the conventional EOMF are shown. These properties are compared with the characteristics of the proposed system with multiple desired users. The performance of desired user 1 is compared, and the signal arrival angle is set to \(0^{\circ}\). With regard to the signal arrival angles of the other users, scenarios 1 and 2 illustrated in Figure 5a,b are assumed. In scenario 1, the signal arrival angles of the other users are evenly spaced at \(\pm 180^{\circ}\). On the other hand, the other users are assumed to exist within \(\pm 180^{\circ}\) of desired user 1 in scenario 2. That is, the array antenna characteristics are degraded in this scenario. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Detail** \\ \hline Channel Model & AWGN \\ Modulation & BPSK and DSSS \\ Spreading sequence & Gold sequence \\ Spreading factor & 31 \\ Carrier frequency & 760 (MHz) \\ Transmit power & \(1\) (desired user 1), Randomly distributed according to DIR (other users) \\ \(E_{b}/N_{0}\) & 15 (dB) \\ Number of total users & 8, 30 \\ Number of antenna elements & 8 \\ Number of desired users & \(1\) (Conventional EOMF), 2, Half the total number of users \\ Direction of arrival & 0 (degrees) (desired user 1), scenario 1, 2 (other users) \\ Information data length & 10,000 (bits) \\ Step size of NLMS algorithm & 0.01 \\ Number of weight updates & 10,000 (array antenna, linear combiner) \\ Synchronization, normalization & Ideal \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Communication Quality Evaluation Test (CQET) parameters. Figure 5: Situation of each scenario. (**a**) Scenario 1: the signal arrival angles of the other users are evenly spaced at \(\pm 180^{\circ}\). (**b**) Scenario 2: the other users are assumed to exist within \(\pm 180^{\circ}\) of desired user 1. First, Table 5 shows the BER result for scenario 1; the number of total users is eight, and DIR = \(-50\) dB. This finding occurs because bit errors were not detected, except for DIR = \(-50\) dB. From Table 5, the BER is approximately doubled when the number of desired users is two and is approximately three times when the number of desired users is four, compared to the conventional EOMF. In other words, the BER deteriorates as the number of desired users increases. However, it is considered that the performance degradation in the proposed system is not significant compared to the conventional EOMF since no bit error was detected when the DIR was greater than \(-45\) dB. Then, Figure 6 shows the BER result for scenario 1; the number of total users is 30. When the number of desired users is 2, it has almost the same BER performance as the conventional EOMF. On the other hand, the BER performance is slightly degraded compared to the conventional EOMF at DIR = \(-35\) dB or less, when the number of desired users is increased to 15. However, it is considered that the performance difference is small since the bit error is not detected under the condition that DIR is \(-30\) to \(0\) dB. Next, Figure 7 shows the BER result for scenario 2; the number of total users is eight.