A New Measurement and Reporting Mechanism for IEEE 802.16j

In this section, a new measurement and reporting mechanism is designed for IEEE 802.16j Multi-hop Relay network. This mechanism and corresponding messaging design [52-55] have been approved by IEEE 802.16j Relay Task Group and became part of the IEEE 802.16j draft standard [10].

In IEEE 802.16j Multi-hop Relay network, MR-BS and non-transparent RS can transmit preamble for the measurement by subordinate RSs or MSs. However, this is not good enough because of following reasons:

1. Not every RS can transmit preamble (e.g. transparent RS), and other stations cannot discover this kind of RS by preamble scanning.

2. Multiple RSs may transmit the same preamble to perform cooperative diversity and act as a virtual station; therefore, those RSs cannot discover each other and other stations can distinguish the signal strength received from each of thses RSs.

3. For the RSs can transmit preamble but in the same hop, they cannot scan the preamble transmitted by each other. Because they are both in transmit mode when transmitting the preamble and unable to receive the preamble transmitted from each other.

Therefore, a new measurement mechanism is necessary for IEEE 802.16j Multi-hop Relay network for RSs and MR-BSs to discover each other.

The basic idea of the proposed mechanism is given in Figure 27, where an example with one MR-cell is provided. In Figure 27 (a), RS2, RS5 and RS8 transmit the reference signal for the measurement by other stations. If the reference signal transmitted by each RS is the same, the transmission opportunity shall be separated by

each RS can be different, the transmission opportunity can be overlapped as Figure 27 (c).

Figure 27. Examples on (a) proposed measurement mechanism, and the corresponding transmission opportunities for the RSs with the (b) same reference signal and (c) different reference signals.

In IEEE 802.16j Multi-hop Relay network, this measurement mechanism can be achieved by coordinating R-amble (i.e. Relay amble) transmission/measurement. Note that the R-amble is a PN sequence with the same format as preamble [39], but transmitted at the end of downlink relay zone as shown in Figure 14(b). Different R-ambles can be transmitted by multiple RSs or MR-BSs over the same radio resource region and decoded by other stations. Therefore, the stations which cannot discover each other due to aforementioned reasons can perform measurement and neighborhood discovery by R-amble transmission.

Since R-amble transmission is a new idea, there were no legacy messages eligible to coordinate the R-amble transmission and measurement opportunities for MR-BS or RSs. A new message and corresponding signaling procedure is designed for RS neighborhood discovery mechanism in IEEE 802.16j Multi-hop Relay network. Its basic idea is shown in Figure 28.

Figure 28. (a) Instructing R-amble transmission by RS-CD message, (b) the

In Figure 28, the MR-BS multicasts the RS_CD (RS_Configuration-Description) message [53] to RS1, RS2 and RS3. The parameters carried by this message are described as following: Start Frame Number in this message is the frame number index to initiate the subsequent R-amble transmission procedure. Monitoring Duration is the duration of the R-amble transmission in unit of frame. Interleaving Interval is the period which is interleaved between the consecutive R-amble transmission opportunities. Iteration is the number of requested iterating intervals. N_Transmitter is the number of RSs in this multicast group shall transmit R-amble. N_Receiver_RS is the number of RSs in this multicast group shall receive/measure the R-amble.

Amble_Index is the index associated to specific R-amble sequence assigned to each RS.

In Figure 28(a), N_Transmitter=2 means the RSs (RS1 and RS2 in this example) associated with the first two Amble Indexes in following shall transmit the R-amble.

Then, the RS (RS3 in this example) associated with the N_Receiver_RS=1 Amble Index shall receive/measure the R-amble. In Figure 28(b), RS1, RS2 and MR-BS will transmit the R-amble for the measurement by RS3 in frame#3. By defining the parameters Monitoring Duration, Interleaving Interval and Iteration, the same R-amble transmission/measurement pattern can be flexibly repeated as shown in Figure 28(c).

However, there will be a synchronization problem when different MR-BSs send their RS-CD messages individually. It is because the frame number indexes used in different MR-cell are usually different and will not be synchronized in practical systems. Therefore, the frame #m for MR-BS1 and the frame #m for MR-BS2 usually correspond to different time.

A method is also proposed in this dissertation by using a network coordinator to

Figure 29. In this example, the MR-BS1 is instructing RS1 to transmit R-amble at frame #m by RS-CD message. The proposed method is that MR-BS1 also sends the frame index “m” and the Amble Index of RS1 to the network coordinator. The network coordinator has a database to record the difference of the frame number indexes between each MR-cell. Therefore, the network coordinator will translate the frame index “m” to frame index “n” based on the difference between MR-BS1 and MR-BS2. Then it will forward the frame index “n” and the Amble Index of RS1 to MR-BS2, so that MR-BS2 can inform its subordinate RSs to scan the R-amble transmitted from RS1 at frame #n. According to this method, the R-amble transmission opportunities instructed in different MR-cells can be synchronized.

Figure 29. Proposed method to synchronize the R-amble transmission/measurement opportunities in different MR-cells

In summary, the proposed measurement and reporting mechanism can be applied for RSs and MR-BSs to discover each other in IEEE 802.16j Multi-hop Relay network. The typical procedure can be summarized as following steps [52]:

1. First, the MR-BS sends the RS-CD message to the RSs which will be involved in the neighborhood measurement mechanism, and the message is either broadcast, multicast or unicast to these RSs. The 8 LSB bits of frame number shall be set to synchronize the starting time to the RSs. If the RSs involved in this mechanism are in different MR-cell, each of the Start Frame Number sent by different MR-BSs shall synchronize to the same frame time.

2. Second, the stations follow the instruction to transmit/receive the R-amble at the designated frames in each iteration.

3. Third, the RSs report the RSSI or CINR with corresponding amble index by RS_NBR-MEAS-REP to MR-BS.

Chapter 6

A New Path Selection for Multi-hop Cellular