The biggest challenge of using wireless and PON is the resource allocation. After connection is established and data is flowing through the network, it is necessary to convert the resource allocations in the wireless domain, into resource allocations in the optical networking domain. There are three ways to do that efficiently:

 

Direct connection of wireless traffic to the PON termination. This solution is shown in Figure 1 and shows that wireless signal is being digitized and treated as the PON signal. Digitized signal may require more traffic than original radio signal. Signal digitization is achieved using intermediate frequency that converts RF signal to optical signal before optical transmission and converts it back after transmission is done. This method is called “in-PON integration” and is using data encapsulation in order to meet the PON management mechanisms requirements.

 

 

Figure 1. In-PON digitized

 

• Using additional wavelengths is suggested and shown in Figure 2. This solution allows to overlay signal through the PON without using its normal bandwidth. The wireless traffic can be left analog for the transmission, since traffic can be completely different from usual PON traffic.

 

 

Figure 2. Analog overlay

 

• Subcarrier modulator can be used as show in Figure 3. The signal is modulated and then transmitted to the NT. This method can be used for analog or digitized radio signal.

 

 

Figure 3. Analog on subcarrier

 

RoF signal might be delayed because of the signal separation which can cause time-outs of wireless MAC-level protocols. Using R&F (Radio and Fiber) architecture for the PON allows to avoid the problem. In future, MAC-level protocol development might help to increase overall performance and efficiency of the network.

 

Overlay integration and in-PON capabilities are summarized in Table 1. Since overlay integration is using separate wavelength its main benefits are higher bandwidth and analog radio signal support. In-PON however can offer fast extension of the existing PON with wireless services.

 

Table 1. Comparison of Optical-Wireless Integration Modes

 

Parameter	In-PON Integration	Overlay Integration
Wired user bandwidth	Reduced	Maintained
Wireless data unit	Encapsulated	Independent
Wireless data rate	Upper bound by PON capacity	Independent
Extra transmission channel requirement	No	Yes

 

Both modes require centralized management, and offer:

• dynamic bandwidth allocation;
• service mobility provisioning;
• network throughput enhancement;
• high QoS;
• IPs differentiated services support.

Using mobile backhaul for PON is beneficial for service provider, since it removes necessity of the backhaul facilities and provides extended coverage. Eliminating dedicated backhaul network is improving cost savings, but also introduces new problems like PON time synchronization.