 via system-level simulation excluding the L1/L2 overhead. Based on the above methodology, the minimum and maximum values of L1/L2 overhead of IEEE 802.16m were calcu- lated and the results are shown in Table 12-2. The minimum and maximum values are obtained based on the consumption of radio resources by the A-MAP, which may vary from three to ten logical resource units per subframe. It must be noted that the L1/L2 overhead for the case of a 4 X 4 antenna configuration is the same as that for a 4 x 2 antenna configuration in the downlink, since the 4-stream pilot pattern is used in the overhead calculation for the 4 X 2 case. Unlike the system/user peak rate calculation, the number of receiver antennas does not affect the L1/L2 overhead. For the two downlink MU-MIMO cases, i.e., a BS with four transmit antennas and two mobile stations each with two receive antennas, and a BS with four transmit antennas and one MS with four receive antennas, the same pilot pattern is used. TABLE 12-2 IEEE 802.16m L1/L2 Overhead Estimation [2] Assumption Overhead Minimum Fraction Maximum Fraction 10 MHz bandwidth L1 overhead 0.3104 0.3104 CP = 1/8 Total overhead (L1/L2) 0.3532 0.4380 DL 2 X 2 antenna configuration 20 MHz bandwidth L1 overhead 0.2824 0.2824 CP = 1/16 Total overhead (L1/L2) 0.3029 0.3441 DL 4 X 2 antenna configuration 664 CHAPTER 12 Performance of IEEE 802. 16m and 3GPP LTE-Advanced TABLE 12-3 Error Sources and Impacts in the Air Interface [8] Overhead Channel Error Sources Impact on System Operation Downlink/Uplink HARQ Misinterpretation, Transmission (frame or encoder ACK/NACK channel misdetection, or false packet) error or duplicate detection of the HARQ ACK/ transmissions NACK signals Explicit rate indication/ Misinterpretation of rate/ One or more transmission errors due mode selection mode selection to decoding at a different rate (modulation and coding scheme) or selection of a different mode User identification channel A user tries to decode One or more transmission errors due a transmissions belonging to to 