Write short notes on WiMAX.

Or Discuss WiMAX. What are the main differences between IEEE 802.11b (WiFi) and WiMAX?

1 Answer

1. WiMAX:

i. The ‘World Interoperability for MicroAcess, Inc. (WiMAX)’ forum, an industry group, focuses on creating advanced technology solution for high speed wide area internet access.

ii. The WiMAX product certification program ensures interoperability between WiMAX equipment from vendors worldwide.

iii. WiMAX can serve as a backbone for 802.11 hotspots for connecting to the internet. Alternatively, users can connect mobile devices such as laptops and handsets directly to WiMAX base stations. Mobile devices connected directly can achieve a range of 4 to 6 miles.

iv. There are 2 types of WiMAX, fixed WiMAX(IEEE 802.16d-2004) and mobile WiMAX(IEEE802.16e-2005). Fixed WiMAX is a point-to-multipoint technology, whereas mobile WiMAX is a multipoint-to-multipoint technology, similar to that of a cellular infrastructure.

2. Some of the salient features supported by WiMAX are:

i. High data rates: - WiMAX can typically support data rates from 500 Kbps to 2 Mbps. - The inclusion of multi-input multi-output(MIMO) antenna techniques along with flexible sub-channelization schemes, advanced coding and modulation all enable mobile to support peak downlink data rates of 63 Mbps per sector and peak uplink data rates of up to 28 Mbps per sector in a 10 MHz channel.

ii. Quality of service (QoS):

  • WiMAX has clearly defined QoS classes for applications with different requirements such as VoIP, real time video streaming, file transfer and web traffic.

iii. Scalability:

  • Mobile WiMAX is designed to able to work in different channelization from 1.25 to 20 MHz to comply with varied world-wide requirements.

iv. Security:

  • There is support for diverse set of user credentials like SIM/USIM cards, smart cards, digital certificates, username/password schemes.
  • All this is based on relevant ‘extensible authentication protocol (EAP)’ methods for credential type.

v. Mobility:

  • Mobile WiMAX supports optimized handoff schemes with latencies less than 50ms to ensure that real time applications such as VoIP can be performed without service degradation.

  • Flexible key management schemes assume that security is maintained during handoff.

3. WiMAX Physical Layer (PHY):

i. For bands in 10-66GHz range, 802.16 defines one interface called Wireless MAN-SC

ii. For 2-11GHz (both licensed and unlicensed):

  • Wireless MAN-SC (single carrier modulation)
  • Wireless MAN-OFDM (256 carrier OFDM with access to different stations using TDMA)
  • Wireless MAN-OFDM (2048 carrier OFDM by assigning subset of carriers to individual station)

iii. WiMAX PHY features include ‘Adaptive Modulation and Coding (AMC)’, ‘Hybrid Automatic Repeat Request (HARQ)’, ‘Channel Quality Indicator Channel (CQICH)’ which is a feedback channel.

iv. All these features provide robust link adoption in mobile environment at vehicular speeds in excess of 120Km/h.

4. WiMAX Medium Access Control (MAC):

i. Each subscriber station need to compete for media only one (for entry).Then, WiMAX base station provides time slot to each subscriber station which may increase or decrease depending on need.

ii. There is a scheduling algorithm for service to each station. This algorithm is robust and not affected by over loading and over subscription.

iii. WiMAX supports different transport technologies such as IPv4, IPv6 and Ethernet.

iv. WiMAX mesh networking allows subscriber stations to communicate with each other i.e. “Subscriber” mode and with base station i.e. “base station” mode simultaneously.

5. Spectrum Allocation for WiMAX:

i. The biggest spectrum segment for WiMAX is around 2.5GHz.

ii. The other bands are around 3.5HZ, 2.3/2.5GHz, or 5GHz, with 2.3/2.5GHz.

6. Other features:

i. The mesh mode of WiMAX enables subscriber stations to relay traffic to one another. Thus, a station that does not have line-of-sight with the base station can get its traffic from another station.

ii. WiMAX technology can provide fast and cheap broadband access to markets that lack infrastructure (fiber optics, copper wire), such as rural areas and unwired countries. WiMAX can also be used in backup during disasters, which may lead the wired networks to get broken down.

iii. As mobile WiMAX is scalable in both radio access and network architecture, it provides flexibility in network deployment options and service offerings.

iv. Mobile WiMAX based on 802.16e uses OFDMA in which carriers are divided among users to form sub channels. The coding and modulation are adapted separately for each sub channel.

v. SOFDMA is an enhancement of OFDMA that scale the number of subcarriers in a channel with possible values of 128, 512, 1024, and 2048.

vi. 802.16e includes power-saving and sleep modes to extend battery life if mobile devices.

vii. 802.16e also supports hard and soft handoff to provide users with seamless connections as they move across coverage areas of adjacent cells.

7. Difference between Wi-Fi and WiMAX:

Sr.No Wi-Fi WiMAX
1. Wi-Fi technology is based on IEEE 802.11 standards. WiMAX technology is based on IEEE 802.16 standards.
2. 802.11a-OFDM,maximum rate=54Mbps.,802.11b-DSSS,maximum rate=11Mbps.,802.11g-OFDM,maximum rate=54Mbps. 802.16-OFDM, maximum rate=50Mbps.,802.16e-OFDM, maximum rate~30Mbps.
3. The stations gain access to media based on CSMA/CA and back off algorithm schemes. There is time slot for each station and there is scheduling algorithm used by base station.
4. Range is less than 100 meters. A kilometer non-line-of-sight, more with line-of-sight.
5. Indoor Environment. Outdoor Environment.
6. No Quality of Service. Five Quality of service enforced by base station.

Fig13. Mesh mode in IEEE 802.16 (WiMAX)

Fig13. Mesh mode in IEEE 802.16 (WiMAX)

Fig14. Applications of IEEE 802.16 (WiMAX)

Fig14. Applications of IEEE 802.16 (WiMAX)

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