Saturday, September 10, 2011


A major feature of WiMAX compared to other wireless access technologies is that it breaks the barrier of addressing a single customer profile. Global system for mobile communications (GSM)/universal mobile telecommunications system (UMTS) provide mainly voice and low speed internet to mobile subscribers, while local multipoint distribution service (LMDS)/wireless local loop (WLL) offer higher bandwidth services to fixed subscribers. WiMAX can offer broadband services to all fixed, nomadic, and eventually mobile subscribers, according to the aims of the latest IEEE 802.16e standard. This major advantage for WiMAX technology offers greater flexibility and scalability; however it presents more design challenges. A conceptual presentation of deployment scenarios, based on equipment, services, and potential customer profiles is presented in Figure 1. Each “sector” represents a WiMAX terminal profile:
  • Fixed-outdoor units (including antenna, RF subsystem, modem), which can be installed on the rooftop or outer building walls for maximizing link performance. A cable connects the unit to an indoor interface terminal that provides Ethernet and VoIP ports.
  • Fixed/portable indoor units (intergraded antenna, RF baseband and interface in a single box), which are installed indoors close to a window or the outer wall. The unit is portable within the indoor space, however it requires power supply.
  • Nomadic/mobile units (PCMCIA cards, handheld devices), which are truly portable (mobile in future versions) and can be used in outdoor and indoor spaces.
Figure 1: Abstract of WiMAX deployment scenarios.
Each terminal profile is built with different performance capabilities and cost towards specific customer profiles. Fixed-outdoor terminals are capable of long range, robust links that can transfer high-bandwidth and delay sensitive services with low impact on network air-interface resources, hence they are more suitable for corporate, small-to-medium enterprises (SMEs), and small-offices-home-offices (SOHOs). The higher hardware and installation costs are balanced by higher revenues. Fixed-indoor terminals have considerably less cost and are self-installable, albeit with smaller link range. Such terminals address the mass market of residential access. Finally the nomadic and portable terminals require even greater network design margins and usually address individual customers at specific service areas (such as community/camp networks). Observing Section 1 it can be seen that business customers are likely to prefer a combination of fixed-outdoor and nomadic units, while residential and personal customers will probably select either a fixed-indoor or a nomadic unit. As WiMAX technology progresses, more system gain will be achieved in the air-interface thus resulting in higher cell ranges and increased percentage of nomadic terminals mainly at the expense of fixed-indoor units.
The continuous development of WiMAX technology from IEEE 802.16-2004 standard to the IEEE 802.16e amendment, has led to significant improvements in the air-interface. Recent advances include higher BS transmit power, advanced antenna systems (MIMO, beamforming (BF)), improved radio resource management through the OFDMA profile, improved coding techniques which reduce the signal-to-interference and noise ratio (SINR) thresholds, efficient uplink (UL) subchannelization, and flexible frequency reuse. The current amendment of WiMAX offers more than 15 dB increase in the system gain over previous versions which drastically extends the radio coverage, and can therefore reach indoor customers even when using portable/mobile terminals. As the WiMAX system gain increases due to the continuous enhancement of the air-interface, in the context of dimensioning, the network size for a specific deployment is reduced, and so is the up-front investment.
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