Cross Layer Design of
Heterogeneous Virtual MIMO Radio Networks
with Multi-Optimization
Wei Chen*, Heh Miao, Liang Hong, Jim Savage, Husam Adas
Dept. of Computer Science
Tennessee State University, USA
Supported by AFRL
APDPM 2010
Outline
Introduction to MIMO &Virtual MIMO Technology
 Problem Statement
 Cross-Layered Design of Virtual MIMO Radio Networks
 Virtual MIMO Network Modeling
 Cooperative Communication Schemes
 Formation/reconfiguration of Virtual MIMO networks
 Routing Backbone and Protocols
 Testing and Evaluation
 Summary and Future Work

Introduction to Virtual MIMO technology
MIMO Technology
Without using extra energy and channel, a MIMO transceiver can be used to
 Extend communication range or reducing error rate (diversity gain)
 Provide higher data rate (multiplexing gain)
MIMO transceiver
T×1
R×1
T×2
R×2
T×M
R×M
Wireless MIMO network
diversity gain
multiplexing gain
However, it is unrealistic to equip multiple antennas to small and
inexpensive wireless devices (e.g., crossbow sensor nodes).
Introduction to Virtual MIMO technology
Cooperative Communication/ Virtual MIMO Technology
 Distributed individual single-antenna nodes cooperating on
information transmission and reception as a multiple antenna array
one 4×2 MIMO link
one 2×3 MIMO link
B
A
First hop
C
Other hops
Problem Statement
Previous Works
 Communication Schemes: MIMO scheme, MISO scheme
 Architecture of Virtual MIMO Network: Homogeneous – the size and
diameter of each virtual MIMO node are same, the distance between of virtual
MIMO nodes are the same. It is possible only when the cooperative nodes are
manually deployed and the topology never changes.
(Reference [7,8])
This Research
Design of heterogeneous virtual MIMO network including
cooperative communication scheme, formation and
reconfiguration of virtual MIMO network and routing
protocol to leverage MIMO technology in a cross-layer
fashion to optimize latency, energy consumption, QoS and
network lifetime.
Virtual MIMO Network Modeling




Underlying network: Network G = (V,E) of single-antenna radio nodes.
d-Clustering: A node disjoint division of V, where the distance between two nodes in
a cluster is not larger than d. The clusters are called virtual MIMO nodes, and the
nodes of G are called primary nodes.
D-Virtual-MIMO links: Let A and B be two d-clusters, and A’ and B’ be the subsets
of A and B, respectively. Suppose there are mt nodes in A’ and mr nodes in B’. If the
largest distance between a node of A’ and a node of B’ is not larger than D, a Dmt×mr virtual MIMO transmission link can be defined between A and B. According
to mt = mr = 1, mt > 1 and mr = 1, mt = 1 and mr >1, mt > 1 and mr > 1, the virtual
MIMO link is called SISO link, MISO link, SIMO link and MIMO link, respectively.
Heterogeneity: The number of primary nodes in the cluster, the diameter of a cluster,
and the length of virtual MIMO links can be different.
MIMO Link
MISO Link
SIMO Link
SISO Link
3×2 MIMO link
Cooperative Communication schemes
– Design

Proposed Multi-MISO Scheme
d
three 4×1 MISO links
three 4×1 MISO links
B
A
B
C
D
Other hops
First hop
Step 1 (Local transmission at A): Each node i in A broadcasts information to all the other local nodes
using different timeslots.
Step 2 (long-haul transmission between A and B): Each node i in A acts as the ith antenna encoding
the sequence using the mt×1 MISO code system. All mt nodes in A broadcast encoded sequence to
the nodes in B at the same time. Each node of mr nodes in B receives mt encoded sequences, and
then decodes them back to according to the mt×1 MISO code system.
MIMO Scheme (Cui et al)

one 4×2 MIMO link
MISO Scheme (Yuan)
one 3×1MISO link
one 2×3 MIMO link
B
A

C
Other hops
C
B
A
D
First hop
one 3×1 MISO link
First hop
Other hop
Cooperative Communication schemes
– Evaluation
(1) Energy per bit for local transmiss ion at virtual MIMO nodes
12( 2b  1)
b

2
constellation size
(2b  1) 4(1  2 )
1
e (r , n, d , x, b) 
N f
ln
G1d  M l  (( Pct  xPcr )  2 PsynTtr / n)
b
bPb
br
1.05( 2b  1)
(2) Energy per for long - haul transmiss ion between vi rtual MIMO nodes
intra
e
inter
2
3( 2b  1) (4D) 2
u
v
1
(r , D, x, y, u , v, b)  E b (b, x, y)
M
N

{
a
+
b
+
c
}Ton / n
l
f
2
b
G
G

br
br
br
( 2  1) t r
Energy consumption and Latency for Multi-MISO scheme
mt
EMultiMISO   n e
i 1
intra
i i
(r , n, d , mt  1, b)  e
mt
inter
(r , D, mt,1, mt, mr, b) ni
i 1
1 mt ni 1 mt
TMultiMISO  (   ni )
B i 1 bi b i 1
Optimize energy consumptio n and Latency
 finding the optimal value of b by minimizing eintra and einter.
Cooperative Communication schemes
– Evaluation
First hop
Other hops
Formation/Reconfiguration of Virtual MIMO networks
– formation of virtual MIMO nodes
Algorithm 1 Formation of d-Clusters
Input: Network G = (V,E) of single-antenna radio nodes, and communication range d/2.
Output: node-disjoint clusters; the diameter of clusters is not larger than d.
Each node u executes the following rounds:
Round 1: u broadcasts its ID, and receives the IDs from its neighbors.
Round 2: (1) u selects a node v with the smallest ID in the received IDs to be u’s CH.
(2) u transmits head declare message (u, v, “head-declare”) to v, and receives the head
declare messages from its neighbors.
Round 3: (1) In the received messages, if u finds any neighbor v who declares u as v’s
CH, u sets itself as a CH abd adds v to its member-list. (2) If u is a CH, it broadcasts
message (u, “head-confirm”), and (3) u receives the head-confirmation messages from
its neighbors.
Round 4: If u received messages (v, “head-confirm”) and v is in u’s member-list, u
removes v from u’s member-list.
Formation/Reconfiguration of Virtual MIMO networks
– formation of routing backbone
Algorithm 1 Formation of Routing Backbone (Spanning tree of head nodes)
Input: m CHs, a sink s, and transmission range D
Output: A spanning tree of the m CHs with the sink as the root; the distance between two
neighboring CHs in the backbone is not larger than D.
Sink s executes the following rounds (finding the children):
Round 1: s broadcasts (s, “find children”), changes its status to “reception”, and receives the
responses.
Round 2: If s receives message (u, s, “child”), s adds each u to its children list;
Other node u executes the following rounds (Selecting the parent and finding the children)
(1) If u received (v, “find children”) from nodes v and u hasn’t decided the parent yet, then u
selects one node w from those nodes to be u’s parent; (ii) u transmits (u, w, “child”) to w ;
(iii) u broadcasts (u, “find children”).
(2) If u has selected the parent and u received messages (v, u, “child”), u adds v to u’s children
list.
Formation/Reconfiguration of Virtual MIMO networks
– Reconfiguration
Algorithm 3 Head-Rotation (u: CH node, e: energy threshold, d:
transmission range in clusters)
u checks its battery energy;
if u’s energy level is lower then u selects a CM v from its cluster
which has the largest energy level; u broadcasts a headrotation request “new head is v” using transmission distance
d; when v received the request and information from u, v
changes its status to be CH, and delete u from its member list;
when u’s any other member w received the request from u, w
changes v to be its CH.
Algorithm 4 Link-Jumping (u: CH node)
u broadcasts a link-jumping request with the ID of u’s parent v and
transmission range of u and v using transmission range max{d(u,x) |
x is u’s backbone neighbor and d(u,x) is the transmission range of u
and x}.
When u’s any child w receives the Link-jumping request, w sets u’s
parent v to be the parent, and sets the transmission distance from w
and v to be d(w,v) = d(w,u)+d(u,v).
Link jumping
Head rotation
Testing and Evaluation
Underlying network: single-antenna nodes are randomly deployed in 400m×400m field
Average size of virtual MIMO nodes: 2 – 4
Diameter d of virtual MIMO nodes: 2m – 10 m
Bandwidth: 10 k – 20k
Transmission range D of virtual MIMO links: 50m – 150m
Task: four source data with 20K bit each are relayed back to the sink
Comparison: Energy consumption and latency in schemes of Chen, Cui, Yun and traditional
(tra) non-cooperative approaches, respectively.
Conclusion and Future works
Summery
 Multi-MISO scheme minimizes the intra communication in virtual MIMO
nodes. It saves energy and reduces latency simultaneously.
 Virtual MIMO nodes/links are allowed to be heterogeneous in order to apply
the visual MIMO technology to any single-antenna radio network.
 The proposed routing backbone simultaneously optimizes energy and latency
along the route.
 The network is reconfigurable with low cost.
Future work
 The proposed virtual MIMO network is reconfigurable. It shall have a very
long network lifetime comparing with other virtual MIMO networks. We
leave the evaluation to the future work.
Homework and assignment
1.
2.
3.
There are two clustering approaches: star-graph based clustering and completegraph based clustering. Discuss the tradeoff on backbone size, latency, and
efficiency of architecture reconfiguration, respectively.
In this research, the cluster-based architecture doesn’t use gateway nodes (cluster
heads connected with cluster heads). Does it make sense and why?
Find the application of multiple antenna array (smart antenna) in daily life.