Prioritization of Patient Vital Signs Transmission Using Wireless Body Area Networks - E-Healthcare Systems and Wireless Communications - page 271

2. Select the optimal channel in terms of link
quality;
3. Allow simultaneous transmissions on dif-
ferent channels in the neighborhood.

Let us assume that i needs to route a packet to
some destination D ; CQBR works by selecting
the optimal available next hop with the best RQI
as,

*

Let us define the Route Quality Indicator
RQI SD , a metric to measure the route quality from
source S to D , as

j = arg max RQI , (3)

j N i ∈ ( ) ijD

where N(i) is the set of i i's non-busy neighbors
(estimated by looking into the overheard RTS/CTS
packets with the data packet length) and RQI ijD
is the RQI value of the route from i to sink D via
j . Then, it utilizes MQ-MAC to select the best
channel and to forward the packet to the next hop.
The routing tables needed by the protocol to
properly operate, LQI TX and LQI RX , are created
and maintained as follows:

c

RQI = min max LQI , (2)

SD ( , ) i j R ∈ c ACH ∈ ij

SD ij

where (i, j) is the link from i to j , R SD is the set
of links along the route from S to D , ACH ij is the
set of available channels for link (i, j) , and LQI i c
is the LQI from i to j via channel c . A route with
higher route quality indicator means the bottleneck
link of this route has higher link quality. This
ensures the nodes can select a route that won't
have a very bad bottleneck link. Compared to the
greedy approach that just forwards to the neighbor
with the highest LQI (without considering the
whole route), our approach offers a way to avoid
bad bottleneck links. For example, a neighbor
with good incoming links but bad outgoing links
should not be the next hop if it is not the destina-
tion. Our CQBR algorithm can avoid using this
node while it may be selected as the next hop in
the greedy approach.
By combining routing and MQ-MAC, we ob-
tain a cross-layer protocol, CQBR, which selects
the next hop based on both the RQI estimated at
the transmitter and the best LQI channel measured
at the receiver . When a node needs to route traffic
to the sink, it selects the best next hop using RQI
in the routing table (Table 4), i.e., data traffic is
forwarded to the neighbor that has the best RQI.
Then with the MQ-MAC protocol, the selected
next hop commands the transmitter to tune to the
optimal channel for data forwarding. Note that
the number of hops to sink is used by the hybrid
scheduler (Sect. 4.4) to estimate the maximum
tolerable delay for the packets at current node.

• Initialization: Channels are scanned and

LQI RX is created at each node. This table
is then broadcast for the neighbors to cre-
ate their LQI TX tables. Routing table is cre-
ated from LQI TX with only the entries to
neighbors;

• LQI RX is updated upon reception of packets;

• Periodically, LQI RX and routing table are

broadcast to neighbors;

• Update LQI TX with LQI RX 's from the

neighbors;

• Update routing table with LQI TX and rout-

ing information from neighbors.

The e2e performance of our MQ-MAC with
CQBR routing (MQMAC-CQBR) in terms of

Table 4. Routing Table at Node i

Destination Next Hop Route

Quality

Hops to Sink

RQI ij 1 1

d 1 j 1 n 1

RQI ij 2 2

d 2 j 2 n 2

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