[Part 1 begins with an introduction and a look at IEEE 802.16M mobile station (MS) state diagrams.]
4.1.2 Access State
Once the mobile station selects a suitable cell, it proceeds to the Access State to complete the network entry/re-entry procedures. Figure 4-4 shows the Access State procedures. The first step is to perform the initial ranging and uplink synchronization with the base station.
The initial ranging is the process of acquiring the correct timing-offset, frequency-offset, and transmit-power adjustments so that the MS uplink transmissions are aligned with the BS uplink frame. The physical layer processing delays are relatively constant and the variations are accounted for in the guard time. The initial contention-based ranging consists of the following steps :
- The MS selects a ranging opportunity using random backoff based on a binary truncated exponential algorithm.iv After selecting the ranging opportunity, the MS chooses a ranging sequence (alternatively known as ranging preamble) from the set of permissible initial ranging sequences. The selected ranging sequence is sent to the BS within the selected ranging opportunity.
- The BS responds with ranging acknowledgement MAC control message within a time interval from the frame where at least one initial ranging preamble code is detected. This message provides responses to all successfully received and detected ranging preamble codes in all the ranging opportunities in a frame indicated by the frame identifier. If all the detected ranging preamble codes indicate "success" status, the BS provides uplink bandwidth allocations for each detected ranging preamble code within a certain time interval. If the MS receives neither the ranging acknowledgement message (corresponding to the initial ranging preamble code and opportunity selected by the MS) nor uplink resource allocation, it assumes that its initial ranging request has failed and restarts the initial ranging procedure.
FIGURE 4-4 Access state procedures in the IEEE 802.16-2009 standard and IEEE 802.16m 
- The initial ranging attempt by the MS may result in three possible outcomes that are signaled via the ranging acknowledgement message (i.e., the message contains ranging status indications from the BS to the MS) as follows:
- The initial ranging preamble code was not successfully detected by the BS or the BS has determined that uplink transmission adjustments are necessary; therefore, the BS provides the required time, power, and possibly frequency adjustments to the MS ("continue" status).
- The initial ranging preamble code was successfully detected by the BS and the BS may provide the MS with time/frequency/power adjustments or uplink bandwidth allocation in order for the MS to send a ranging request message ("success" status).
- The initial ranging preamble code may or may not have been successfully detected by the BS and the BS requests the MS to abort the ranging process ("abort" status).
- Based on the outcome ranging response, the MS takes the following actions:
- Upon receiving a "continue" status indication and adjustment parameters in the ranging acknowledgement message, the MS adjusts its uplink transmission parameters according to the instructions by the BS and continues the ranging process by sending a ranging preamble code randomly chosen from the initial ranging code-set (using random selection rather than random backoff) in the initial ranging opportunity.
- Upon receiving a "success" status notification, the MS waits for uplink bandwidth allocation. If the MS does not receive bandwidth allocation within a certain time interval after sending the ranging preamble code, it restarts the initial ranging procedure, or it may return to downlink synchronization stage again. If the MS receives uplink bandwidth allocation, it sends a ranging request message. If the granted bandwidth allocation cannot accommodate the entire ranging request message, the message may be fragmented in order to fit to the allocated resources, and the MS may further request additional resources for the remaining message fragments. In response to the bandwidth request, the BS provides uplink allocation via a downlink control information element where the MS is identified by the same Random Access Identifier (RA-ID) that was used for the previous allocation. This RA-ID is used until completion of the ranging response. If the MS does not receive bandwidth allocation, or the ranging request and response message exchange are not completed within 128 frames, the MS re-sends the ranging preamble code and reinitiates the initial ranging procedure.
- The BS assigns temporary STID (TSTID) to the MS via the ranging response message upon successful ranging. The initial ranging process is concluded after receiving the ranging response message. The TSTID is used until permanent STID is assigned following successful registration.
In the case where the IEEE 802.16m mobile and base stations are interfaced with a legacy ASN, the actual MAC address is included in the ranging request message similar to that of the legacy systems , because the IEEE 802.16m station identifiers are not recognized by the legacy ASN. Immediately after completion of the initial ranging, the MS informs the BS of its capabilities by transmitting a capability negotiation request message with its capabilities set to "on."  The BS responds with a capability negotiation response message with the intersection of the mobile station's and the base station's capabilities set to "on."
The problem with this way of capability negotiation in IEEE 802.162009 standard is that the length of the messages can grow excessively large without the possibility of fragmentation (this problem has been fixed for some MAC management messages that can be fragmented in the latest revision of the standard ), resulting in increasing error probability and reliability issues for the cell-edge users. Furthermore, the BS and the MS are unnecessarily required to negotiate some capabilities and parameters that are required for normal operation of the system, resulting in inefficient use of radio resources, increased network entry/re-entry latency, and compromising reliability.
ivThe binary exponential backoff or truncated binary exponential backoff refers to an algorithm used to space out repeated re-transmissions of the same block of data. As an example, the re-transmission of frames in Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) and Carrier Sense Multiple Access with Collision Detection (CSMA/CD) networks, where this algorithm is part of the channel access method used to send data over these networks. The re-transmission is delayed by an amount of time derived from the slot time and the number of attempts to re-transmit. After n collisions, a random number of slot times between 0 and 2n - 1 is chosen. For the first collision, each sender might wait 0 or 1 slot times. After the second collision, the senders might wait 0, 1, 2, or 3 slot times, and so forth. As the number of re-transmission attempts increases, the number of possibilities for delay increases. The "truncated" simply means that after a certain number of increases, the exponentiation stops, i.e., the re-transmission timeout reaches a ceiling, and thereafter does not increase any further .