Integrated Wireless-pon access Network Architectures Milos Milosavljevic

Figure 8-3: An example of xPON backhauling for LTE [22]
In addition to the above, the architecture presented in this thesis is based on the assumption that 
a frequency reuse pattern of 1:3:3 is used where each base station antenna covers three sectors 
operating at different frequencies. However, in some recent deployment scenarios frequency 
reuse of one has been considered where each sector is supported by the same frequency. In this 
case, additional LOs are needed at an ONU/BS for each sector in order to avoid interference 
with other base stations addressed with FDM on the same PON. Also, in order to reduce 
interference in overlapping sectors caused by the frequency reuse pattern of one, in a similar 
manner to co-ordinated scheduling, efficient network management at the CO without 
introducing unnecessary delay into the system should be investigated.

---

Chapter 8 Project Achievements and Future Work 
163 
Finally, as an alternative to RoF a digital-over-fibre (DoF) variants could be considered as well 
where analog wireless RF/IF data are first digitised prior to transmission over the fibre. This 
offers the advantages of exploiting mature digital optical communications hardware and 
network interfaces while providing for a high performance microwave signal distribution 
framework [23]. However, as a direct result of digitization, the data rate of the optical link is a 
product of sampling resolution and the sampling frequency. The relative cost advantage of DoF 
over analog RoF from the optoelectronics perspective will depend on whether the data-rate or 
the maximum RF frequency is high. In FDM systems the sampling rate depends strongly on the 
wireless RF frequencies as well as their fractional bandwidth used to carry data. As the RF 
frequency increases when applications move to high frequency bands, the implementation of 
DoF becomes more challenging.
Firstly, the electronic sampling sub-systems need to be able to accommodate these high RF 
frequencies increasing their cost in parallel with that of the RF. The second aspect arises from 
the fact that overall data rate for the digital optical link can be excessively high, thereby 
negating the cost benefit of DoF over analog RoF implementations [23].
On the other hand, digital transmission based on the CPRI [24] is clearly allowing deployment 
of distributed base station antennas with high flexibility and low deployment cost. The CPRI 
technology is defining key internal interface of radio base stations between the Radio 
Equipment Control (REC) and the Radio Equipment (RE), as shown in Figure 8-4. With a clear 
focus on layer 1 and layer 2 the scope of the CPRI specification is restricted to the link interface 
only, which is basically a point to point interface. Such a link shall have all the features 
necessary to enable a simple and robust usage of any given REC/RE network topology, 
including a direct interconnection of multiport REs. To that extent CPRI provides for simple 
remote radio heads since all the signal processing is performed centrally. 

---

Chapter 8
The main drawback of this solution is in order to support the most recent OFDMA
standards such, as WiMAX and LTE with 20 MHz bandwidth, the total throughput required on 
the optical link is in the range of 2.5 Gbits/s. Therefore, high bandwidth backha
required. 
It can be concluded from the above
variants on the same integrated architectural platform could be beneficial and should be 
investigated further.