Network Entry in IEEE 802.16j-2009

An MS under an MR network would undergo the same procedures for network entry, initialization, and periodic ranging as it would in a PMP network. To achieve this compatibility, there are operations to be noted by the MR-BS and the RS in order to maintain a non-MR activity for the MS. As such, operations made on part of an MS during these procedures will not be discussed in this section. The scope of this section hence will comprise two sets of descriptions, a description of the actions taken by an MR-BS to carry out MS procedures, and a description of the procedures required for RS operation. An RS naturally requires additional steps to become fully operational. Figure 5.2 schematizes the network entry and initialization procedures for an RS. The standard distinguishes eleven major steps, with four additional sub-procedures required for RS. In the following list, the optional procedures are marked with an asterisk (*). A distinction is also made between the procedures required for SS only or RS only.

1. Scanning and synchronization;

   a1. Performing first stage access station selection (RS only);

2. Obtaining transmission parameters from UCD message;
3. Ranging;
4. Negotiating basic capabilities;
5. Authorizing SS/RS and performing key exchange*;
6. Performing registration;

   f1. Obtaining neighbor station measurement report (RS only)*;

   f2. Performing the second station access selection (RS only)*;

   f3. Path creating and tunnel establishment (RS only)*;

7. Establishing IP connectivity*;
8. Establishing time of day*;
9. Transfer operational parameters*;
10. Setting up connections (SS only);
11. Configuring operation parameters (RS only).

In addition, in an accelerated network entry operation for RSs called RS network entry optimization, an MR-BS may instruct the RS to omit procedures d–f (1–3), and k.

RSs follow the same scanning and synchronization procedures as SSs. An RS may optionally store preamble indexes and corresponding signal strengths, and report them if requested by the MR-BS during procedure f1.

To assist the first stage access selection, an MR-BS and operating RSs may transmit a TLV with an end to end metric in the DCD. This metric would be considered in an entering RS's decision to select an access station. Once an access station is selected, the RS carries on with the network entry procedure.

Figure 5.2 Network Entry and Initialization flowchart for IEEE 802.16-2009. An adaptation from Figure 65a, page 102 in 16j-2009 “RS Initialization”. Reproduced by permission of © 2009 IEEE.

MR-BSs and RSs involved in registration shall perform as described in PMP. However, if the MR-BS decides that neighbor measurement report is required, the entering RS shall provide the report with the requested details. Once the RS has sent a REG-REQ to the MR-BS, it shall wait for a REG-RSP.

A neighbor station measurement report can include the signal strengths and the respective preamble indexes of neighboring ntRSs with unique BSIDs or signal strength and R-amble indexes of neighboring tRSs or ntRSs with shared BSIDs. When measurements are not required, the RS skips both reporting and the second stage access selection and proceeds to the next procedure indicated in the MR-BS's RNG-RSP message. Note that mobile RSs may be instructed as to which preamble indexes should they collect the measurements for. If an RS is requested to report measurements, the MR-BS shall not change the frame configuration for the RS's superordinates before the RS becomes fully operational.

The purpose of the optional second stage access station selection is to direct the entering RS to another access station for network and resource management objectives like interference management or load balancing between relay paths. This procedure depends on the neighbor measurement report. If the entering RS is to associate with the access station selected in the first stage, it shall proceed with remaining network entry procedure. If the current access station is changed to another that is under the same MR-cell, the MR-BS shall indicate the new station's preamble index to the RS, and both the MR-BS and the RS will be engaged in a network reentry procedure (for which network entry optimization may be applied). If the network reentry fails, the originally selected access station shall be used as a first candidate for reentry.

The optional path creation and tunnel establishment procedure can be used to create a path, establish tunnels or bind tunnels to an already active path, and is performed after an RS successfully completes the process for access RS selection. Single tunnels can only be used for either management or transport.

Initial Ranging

As the SS carries on the initial ranging procedures described above, the MR-BS and the RS need to manage the relevant signaling in a seamless manner with respect to the SS. Subtle differences in behavior largely depend on network configuration, that is, whether SS is performing initial ranging through a tRS or an ntRS, whether the implemented scheduling is centralized or distributed, and whether a group of RSs share a BSID or each RS has its own unique BSID. As will be noted below, an RS initial ranging procedure closely resembles that of an SS except for certain modifications.

In a network where a tRS is connected directly to an MR-BS, the RS monitors the ranging channel on the access link for initial ranging codes. The codes are then relayed to the serving MR-BS with proper adjustments (for time, power, etc) in an MR_RNG-REP. The MR-BS, in turn and after waiting for MR_RNG-REP from other stations, decides on the best path for the SS. If adjustments are required, the MR-BS sends an RNG-RSP to the SS. Otherwise; the MR-BS makes an allocation in the access uplink for the SS so that it would send its own RNG-REQ.

If the tRS is attached to the MR-BS through a centralized ntRS, the tRS monitors the ranging channel in the UL-MAP set by its superordinate station. The ntRS then manages the tRS's MR_RNG-REP, schedules downlink allocation to send the RNG-RSP to the SS and, upon requiring no further adjustment, request uplink bandwidth for the SS to send its RNG-REQ.

In instances where the SS is performing initial ranging with a group ntRSs sharing a BSID, the MR-BS needs to decide whether to specify the access RS as a receiving, or utilize the multicast management CID for the shared BSID group.

When an SS is performing initial ranging through a tRS attached to a scheduling RS, or through ntRSs sharing a BSID, the scheduling RS shall perform adjustments directly with the SS without getting back to the serving MR-BS. The scheduling RS will also independently manage bandwidth allocations for relaying MAC messages to and from the SS.

For ntRSs with centralized scheduling and unique BSIDs, the ntRS monitors the ranging channel. Upon receiving a ranging code, the ntRS shall determine whether adjustments are necessary and, if they are, the ntRS will seek allocation for the RNG-RSP from the MR-BS. If no adjustments are required, the ntRS shall request an uplink allocation for the SS to send its RNG-REQ. The RNG-REQ is ultimately handled by the MR-BS.

When an SS is dealing directly with a scheduling RS, the RS monitors the ranging channel specified in its own UL-MAP. When the RS detects a ranging code on its access link, it shall perform adjustments directly with the SS.

Finally, when an RS is performing initial ranging, it shall follow the procedures described above for the SS except that it will use an RS initial ranging code instead of a regular initial ranging code. After receiving an RS initial ranging code, the MR-BS or the ntRS may send an RNG-RSP indicating preamble indexes of candidate neighbor stations. In all, operating tRSs ignore an RS initial ranging codes.

Note that, similar to IEEE 802.16-2009, the CDMA ranging codes utilized in OFDMA are 256 codes, each consisting of with 144 bits. Each BS is assigned S codes from the 256, that is, the range between S to ((S + O + N + M + L +P + Q) mod(256)) where O, N, M and L are used for normal ranging and P and Q for RS initial ranging and RS unique CDMA ranging, respectively.

Periodic Ranging

Periodic ranging for both SSs and RSs proceeds as in periodic ranging for PMP operation.

For an SS, the ranging completes when the access station (whether an MR-BS or an ntRS) sends the RNG-RSP. For an RS, an MR-BS may assign a dedicated RS CDMA periodic ranging code. Again, the ranging process completes once the access station to which the RS is attached sends an RNG-RSP.

Superordinate stations to an SS/RS may initiate periodic ranging based on measurements. This involves sending an unsolicited RNG-RSP. If the superordinate is a tRS, the MR-BS and tRS shall proceed normally. If the superordinate is tRS or ntRS in an RS group, an MR_RNG-REP is sent to the MR-BS to request that an RNG-RSP be sent (with the necessary adjustments) to the SS. If the superordinate is a centralized ntRS, it will seek the MR-BS for downlink allocation to send the RNG-RSP. Finally, if the superordinate is a scheduling RS, it would send the RNG-RSP directly without going back to the MR-BS.