Integrated Wireless-pon access Network Architectures Milos Milosavljevic

Chapter 2 Next Generation Access Networks 
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support for time division multiple access (TDMA) and frequency division multiple access 
(FDMA) transmission as well as advanced antenna techniques. 
The end-to-end services are delivered over an IP architecture allowing WiMAX to ride the 
declining cost curves of IP processing and facilitate easy convergence with other networks [26]. 
The base stations, usually equipped with multiple antennas employed in various downlink 
multi-antenna schemes such as beamforming, spatial multiplexing or spatial diversity coding 
[23, 26], are connected to the ISP by means of either T1/E1 interfaces, Ethernet or via line-of-
sight millimetre-wave connections [27, 28]. 
Figure 2-2: WiMAX deployment scenario 
As demonstrated in Figure 2-2, each base station is serving a single cell, and is able to transmit 
at the 2.3GHz, 2.5GHz, 3.5GHz and/or 5.7GHz bands depending on regulatory issues [22, 29]. 
For Europe, the 3.5GHz licensed band is typically allocated to service providers [22, 30, 31].
To increase the spectral efficiency across a cell, a frequency reuse technique is employed so that 
each cell is being sectorised and WiMAX base stations accessing the individual sectors with 

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Chapter 2 Next Generation Access Networks 
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directional antennas [23]. An illustration of that is shown in Figure 2-2 where a frequency reuse 
with a factor of 1:3:3 is assumed [23]. However, this approach could impose strong inter-cell 
interference and as a result interference management should be applied with multi-site 
processing [32]. Coordination, via direct communication, between the cooperating base stations 
needs to be established, requiring therefore additional capacity on the backhaul link. 
In addition, the WiMAX signals are broadcasted from a base station to all subscribers in a cell 
or a sector within a radius of typically 3-5 miles [30]. Therefore, due to the inherited point-to-
multi-point (P2MP) distribution, TDMA is typically applied in upstream [33] to serve as the 
required contention control mechanism, similar to TDM-PONs. To reduce the traffic 
congestion, coverage and throughput due to TDMA, more densely spaced base stations with 
improved spectral efficiency and QoS could be deployed resulting, however, in increased 
deployment cost.
Current WiMAX standards include the existing IEEE802.16d [24] and IEEE802.16e [25], 
providing fixed and mobile broadband wireless operation respectively. The main characteristics 
of these standards are summarised in Table 2-1. Compared to initial WiMAX standard 
definitions, IEEE802.16-2001 [34], at the physical layer these standards are operating at 2-11 
GHz transmission bands, licensed and license-exempt, driven by the need for non-line-of-sight 
(NLOS) operation [24, 25]. For efficient multipath propagation mitigation the modulation 
technique utilised is primarily based on orthogonal frequency division multiplexing (OFDM) 
where data is carried over closely spaced orthogonal subcarriers, generated by Fast Fourier 
Transform (FFT), with long symbol duration [23]. Each individual subcarrier is modulated with 
QPSK, 16-QAM or 64-QAM digital modulation formats [23]. In addition a wide range of guard 
times, attached to an OFDM symbol, are defined in the WiMAX standards to allow for the 
necessary trade-off between spectral efficiency and delay spread robustness [24, 25]. The 

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