Wimax standards and Security The Wimax

Download 2,02 Mb. bet 107/186 Sana 29.05.2022 Hajmi 2,02 Mb. #619147

Bog'liq
CRC - WiMAX.Standards.and.Security

Bits/Symbol	10 MHz Bandwidth
20 MHz Bandwidth
BPSK-1/2	96	3.84	7.68
QPSK-1/2	192	7.68	15.36
QPSK-3/4	288	11.52	23.04
16QAM-1/2	384	15.36	30.72
16QAM-3/4	576	23.04	46.08
64QAM-2/3	768	30.72	61.44
64QAM-3/4	864	34.56	69.12

into constant-duration symbols carried on multiple, orthogonal carriers. The bandwidth of the final signal is the frequency range occupied by the carriers. Bandwidth used by 802.16 OFDM may be allocated in the license-exempt 5 GHz frequency band or in other, licensed, frequency bands.
The number of raw bits carried by each OFDM symbol depends on the mod- ulation, coding, and the bandwidth occupied by OFDM during transmissions (Table 8.1). Modulation and coding determine how many bits are carried by each orthogonal carrier, while OFDM bandwidth dictates the duration of the symbols. In 802.16, there are two possible OFDM bandwidths: 20 MHz with
12.5 µs symbol duration and 10 MHz with 25 µs symbol duration. Since the OFDM symbol duration for 10 MHz bandwidth is twice as long as the OFDM symbol duration for 20 MHz bandwidth, the raw bitrate at 10 MHz bandwidth is half of the raw bitrate at 20 MHz bandwidth.
In situations where 802.16 hardware is not available, but QoS in the mesh is still required, it is possible to use 802.16 TDMA technology with properly controlled 802.11 hardware. In Ref. 9, we have shown that it is possible to embed 802.16 MAC packets into 802.11a [10] broadcast packets with insignif- icant overhead. TDM is achieved by fixing the 802.11 back-off mechanism to one slot before every transmission. The back-off time limits can be changed on 802.11 hardware supporting QoS. We have shown in Ref. 9 that the system with embedded 802.16 packets has a performance comparable to the perfor- mance of true 802.16 systems. In Ref. 11, the authors show that drivers of a specific 802.11 network card can be modified so that true TDM is achieved over 802.11 hardware. This is different from the approach in Ref. 9 since it requires that the details of the operation of the underlying 802.11 hardware be available at the MAC layer.

2. 
   
   
   Download 2,02 Mb.
   
   Do'stlaringiz bilan baham: