1. February 19
November 15, 2005
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: TG4a (UWB)2-MAC proposal for UWB-LDR wireless networks
Date Submitted: November 15, 2005
Source: G.M. Maggio (ST) & L. De Nardis, M.-G. di Benedetto (U. di Roma)
Contact: Gian Mario Maggio (STMicroelectronics)
Voice: ,
Abstract: TG4a (UWB)2-MAC proposal for LDR location-aware UWB networks
Purpose: To provide detailed information on (UWB)2-MAC proposal for Low-Data Rate location-aware UWB wireless networks
Notice: This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

2. February 19
November 15, 2005
(UWB)2-MAC Protocol for Low Data-Rate Location-Aware UWB Wireless Networks
Gian Mario Maggio (ST)
&
Luca De Nardis, (U. di Roma)
Maria-Gabriella Di Benedetto (U. di Roma)
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

3. UWB-LDR Specific MAC Design
February 19
November 15, 2005
UWB-LDR Specific MAC Design
Ultra Wideband based on Impulse Radio and Time Hopping is characterized by:
Low probability of pulse collision
Accurate ranging
Medium Access Control can therefore:
Exploit resilience to Multi-Access Interference (MAI) in Low Data-Rate (LDR) applications
Define procedures for bi-directional distance estimation
(UWB)2: Uncoordinated, Wireless, Baseborn
medium access for UWB
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

4. Key Assumptions MAC Design Choices
February 19
November 15, 2005
Key Assumptions
MAC Design Choices
Synchronization is achieved on a packet-by-packet basis
Simple synchronization hardware
(no precise clock requirements)
Low Data-Rate and “rare” packets
(peak rate  1 Mb/s,
average rate  20 Kb/s)
No Carrier Sensing: Pure Aloha
(with TH coding)
TH-CDMA:
Common signaling code available to all devices +
Dedicated data code unique for each transmitter
Need for broadcast packets
Time-Hopping Impulse Radio
with ~GHz BW
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

5. (UWB)2–MAC Key Features
February 19
November 15, 2005
(UWB)2–MAC Key Features
(UWB)2 is a hybrid multi-channel MAC protocol
Each channel is identified with a Time Hopping code
CONTROL packets are transmitted on a Common channel, i.e. using a Common TH-code known to all terminals
DATA packets are transmitted on dedicated channels identified by Transmitter-unique TH codes,
The agreement on the code to be used for a DATA packet is the result of a handshake performed on the Common code
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

6. Impact of (UWB)2-MAC PHY MAC No Carrier Sensing required
February 19
November 15, 2005
Impact of (UWB)2-MAC
PHY
No Carrier Sensing required
Aloha approach can be applied for terminals adopting one TH-code (spread-Aloha), or no TH-coding at all
 When switching between different TH codes is available, the code dimension is used in the protocol
Ranging capability at the PHY is required
MAC
TH-CDMA (vs. TDMA)
Support for ranging primitives
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

7. Backward Compatibility Issues: 802.15.4 vs (UWB)2-MAC
February 19
November 15, 2005
Backward Compatibility Issues: vs (UWB)2-MAC
Data rates of 250 kb/s, 40 kb/s and 20 kb/s
Star or Peer-to-Peer operation
Support for low latency devices
CSMA-CA channel access
Fully handshaked protocol for transfer reliability
 Possible in (UWB)2
 Possible in (UWB)2, as long as a slotted time axis is adopted (guaranteed slots can be defined, as in )
 Possible in (UWB)2, with different channel access strategy; all topologies defined in can be adopted without modifications
 Replaced by Aloha in (UWB)2:
Pure Aloha in Peer-to-Peer operations
Pure/Slotted Aloha in Star operations (slotted time axis provided by the PNC)
 Same as for (UWB)2 (optional ACK is already in the protocol, as in )
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

8. (UWB)2-MAC: Transmission Procedure (1/2)
February 19
November 15, 2005
(UWB)2-MAC: Transmission Procedure (1/2) Tx Rx LE
Sync Trailer
Rx Node ID
Tx Node ID
TH-Code
TH-Flag
LE PDU
CRC
Step 1: Tx node sends a Link Establishment (LE) PDU (Protocol Data Unit) to Rx using the Common TH code. The LE PDU contains:
IDs of TX and RX
Tx TH-Code
Sync. trailer + CRC field Tx Rx LC
LC PDU
Sync Trailer
Rx Node ID
Tx Node ID
CRC
Step 2: Rx node replies with a Link Confirmation (LC) PDU and switches to the Tx TH-Code
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

9. (UWB)2-MAC: Transmission Procedure (2/2)
February 19
November 15, 2005
(UWB)2-MAC: Transmission Procedure (2/2) Tx Rx
DATA
Sync Trailer
Rx Node ID
Tx Node ID
PDU
Number N
PACKETS
PAYLOAD
DATA PDU
CRC
Step 3: Tx node sends the DATA PDU on the dedicated, transmitter-specific TH code communicated in the LE PDU
ACK PDU
Sync Trailer
Rx Node ID
Tx Node ID
DATA Packet
Status Tx Rx
ACK
Step 4: Rx node sends an ACK packet when required by the Tx node (not sent for PDUs transferring broadcast information)
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

10. Aloha vs. Slotted-Aloha
February 19
November 15, 2005
Aloha vs. Slotted-Aloha
Both Pure Aloha/Slotted Aloha were analyzed
Slotted-Aloha could improve performance in centralized network topologies, where the coordinator can provide slot synchronization with low overhead
For NB systems, Slotted Aloha guarantees a higher (up to 2x) throughput w.r.t. Pure Aloha
What about UWB-LDR networks?
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

11. (UWB)2-MAC: Performance Analysis
February 19
November 15, 2005
(UWB)2-MAC: Performance Analysis
Performance of (UWB)2 was analyzed as a function of:
# of users
User data rate, R
Transmission range
Channel model (LOS vs NLOS)
Assumptions:
Impulse Radio (IR) UWB terminals with TH-coding
Ghassemzadeh & Tarokh path loss model
Pulse Collision: MAI model specific for IR-UWB
No FEC was considered (all bits in a packet must be correct, for a packet to be correct)  ARQ (Automatic Repeat on reQuest)
Tx power is selected high enough to study the effect of MAI (impact of thermal noise is made negligible)
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

12. Simulation Settings February 19 November 15, 2005
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

13. (UWB)2-MAC: Performance in AWGN (1/4)
February 19
November 15, 2005
(UWB)2-MAC: Performance in AWGN (1/4)
Impact of # of terminals and transmission range on throughput:
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

14. (UWB)2-MAC: Performance in AWGN (2/4)
February 19
November 15, 2005
(UWB)2-MAC: Performance in AWGN (2/4)
Impact of # of terminals and transmission range on delay:
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

15. (UWB)2-MAC: Performance in AWGN (3/4)
February 19
November 15, 2005
(UWB)2-MAC: Performance in AWGN (3/4)
Impact of transmission range and user data-rate on throughput:
5 Users
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

16. (UWB)2-MAC: Performance in AWGN (4/4)
February 19
November 15, 2005
(UWB)2-MAC: Performance in AWGN (4/4)
Impact transmission range and user data-rate on delay:
5 Users
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

17. (UWB)2-MAC: Performance in Multipath (1/2)
February 19
November 15, 2005
(UWB)2-MAC: Performance in Multipath (1/2)
Throughput vs. channel models (CM1, CM2, CM5,
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

18. (UWB)2-MAC: Performance in Multipath (2/2)
February 19
November 15, 2005
(UWB)2-MAC: Performance in Multipath (2/2)
Delay vs. channel models (CM1, CM2, CM5,
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

19. February 19
November 15, 2005
Conclusions
For UWB-LDR networks both Pure/Slotted Aloha lead to high throughputs (due to MAI resilience and low probability of packet collisions)
Gap increases with traffic (# of users)
Slotted Aloha leads in average to a higher delay (Δ~1ms)
Impact of traffic: Pure Aloha is more sensible  Decreased throughput, higher delay
With multipath: Slotted Aloha does not provide advantages in terms of throughput, but higher average delay
Effect of the channel: Indoor NLOS (CM2) with higher data rate exhibits poorer performances
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto

20. February 19
November 15, 2005
References
M.-G. Di Benedetto, L. De Nardis, M. Junk, G. Giancola, "(UWB)2: Uncoordinated, Wireless, Baseborn, medium access control for UWB communication networks," Mobile Networks and Applications Special Issue on WLAN Optimization at the MAC and Network Levels (2005)
L. De Nardis and M.-G. Di Benedetto, “Joint communications, ranging, and positioning in low bit rate Ultra Wide Band networks,” IEEE INFOCOM 2005 Student Workshop, March , Miami, Florida, USA
L. De Nardis, G. Giancola, M.-G. Di Benedetto, "Power-Aware Design of MAC and Routing for UWB Networks", in Proceedings of the IEEE Global Telecommunications Conference (Globecom), 2004, 19 November - 3 December 2004
Di Benedetto, M. G., and Giancola, G. Understanding Ultra Wide Band Radio Fundamentals. Prentice Hall, 2004
S. S. Ghassemzadeh and V. Tarokh, “UWB Path Loss Characterization In Residential Environments”, IEEE Radio Frequency Integrated Circuits Symposium, pp , 2003
G.M. Maggio, L. De Nardis & M.-G. Di Benedetto