Integrated Wireless-pon access Network Architectures Milos Milosavljevic

Chapter 3 Optical and Wireless PHY Integration
59 
A central symmetry property of the constellation diagram, in specific the statistical equivalence 
of the symbols, such as (I=x,Q=y), (I=-x,Q=-y), (I=x,Q=-y) and (I=y,Q=x), is used to improve 
the data statistics [38, 39]. This is realised by reporting all symbols into a single quadrant 
((I,Q}>0), and performing the SER analysis on this quadrant only. 
Significantly, the constellation mapping for mQAM symbols is based on Gray coding therefore 
the bit error rate (BER) can be easily calculated from the obtained SER by [39]: 
BER 
SER
BitsPerSymbol 3.2
That way, demodulation of complex symbols is not required in order to estimate the BER. 
Detailed implementation of the WiMAX transceivers as they have been devised using the 
VPI/MATLAB co-simulator is presented in chapter 4. 
 
 

---

Chapter 3 Optical and Wireless PHY Integration
60 
3.7 Summary
This chapter introduced highly referenced optical/wireless integration scenarios as they have 
emerged from research initiatives worldwide, followed by the review of possible deployments 
infrastructures. Although the integrated architectural platforms have been employed mainly for 
short range in-home networks (OMEGA, FUTON, OFM techniques, etc.) with only a few 
deployments targeting to connect transparently remote base stations in a point-to-point 
metro/access configuration, it was established that they have not fully concentrated on 
developing access networks, deploying emerging wireless broadband standards, such as 
WiMAX, over standardised point-to-multipoint xPONs aiming to further increase the reach and 
capacity of both networks. 
To define the initial concepts of a wireless backhauling and primarily at this stage the properties 
of its transmission links, it was concluded that RoF reduces unnecessary overheads, typically 
presented in alternative signalling formats such as digital. As a result the specifications of RoF 
signal generation and demonstrated link impairments by means of VPI simulations are 
delivered.
Successively preliminary results were drawn with reference to fibre chromatic dispersion and 
OFDM signal quality estimation in terms of EVM plots. Simulation results have confirmed that 
due to optical double sideband modulation amplitude deeps could occur at certain frequencies 
of the fibre transfer function. Therefore, careful consideration is required in subcarrier selection 
when FDM is applied. Also, due to inherent optical nonlinearities and link noise it was 
suggested that in the presence of OFDM transmission the optical modulator drive powers must 
be carefully selected to meet the stringent requirements at the remote bases stations. 
Finally, VPI/MATLAB co-simulation requirements for WiMAX signal detection and 
generation are presented where wireless digital signal processing will be performed exclusively 

---