and for reader's understanding of the relay station behavior. 4.5 OPERATIONAL STATES OF FEMTO BASE STATIONS A femto BS or femto access node is a base station with a low transmit power, typically installed by a subscriber in home or small office/home office environment to provide access to a closed or open group of users as configured by the subscriber and/or the access provider. A femto BS is connected to the service provider's network via a broadband wired (or wireless) connection and typically operates in licensed spectrum, and may use the same or different frequency as macro base stations. Its coverage may overlap with that of a macro BS. A femto BS may be intended to serve open subscriber groups or closed subscriber groups [16]. Figure 4-22 illustrates the femto BS state diagram. The state diagram consists of the Initialization and Operational States. The Initialization State includes procedures such as configuration of radio interface parameters and time synchronization. After successful attachment to the network, a femto BS enters the Operational State. The Operational State consists of two modes: Normal Mode and Low-Duty Mode. In Low-Duty Mode, the femto BS will be periodically unavailable to reduce the adjacent/co-channel interference neighboring femto or macro base stations. Femto base stations are required to synchronize with the network timing to the extent that synchronization error does not disrupt network operations. They may use different schemes to achieve synchronization with the network depending on the deployment CHAPTER 4 IEEE 802.16m System Operation and State Diagrams Obtain CDMA initial ranging code/ Process CDMA initial ranging code/ Send RNG-RSP (continue) Wait for CDMA initial ranging code Obtained CDMA initial ranging code/ Process CDMA initial ranging code/ Send RNG-RSP (success) or CDMA Allocation IE Obtained CDMA initial ranging Wait for code/Send RNG-RSP (abort) RNG-REQ Obtained RNG-REQ/Process RNG -REQ Obtained RNG-REQ7 Send RNG-RSP (success) Process RNG-REQ re-transmission/ Send R