MAC for Tactical Communication Networks

Hongik University

Byung-Seo Kim

Tactical Communications

Wireless MAC Protocol

Battlefield Tactical Data Links

Link-11

Link-16

Link-22

Two-Way Radio

Wireless Multicast over Tactical Communications

OUTLINES

KRnet 20082

Tactical Communication

Definition

Communications in which information of any kind, especially orders and decisions, are conveyed from one command, person, or place to another within the tactical forces, usually by means of electronic equipment, including communications security equipment, organic to the tactical forces.Battlefield, Public Safety, Disaster Recovery, Mission Critical

Evolutions

Voice oriented traffics

Low Data Rate

Analog Signal

Infrastructure-based

Architecture

Line-of-Sight Communication

Multimedia Traffic

(Voice, Data, Image, Video)

Broad bandwidth

Digitized Signal

Ad-Hoc-based Architecture

NLOS Communication with Multi-Hop

Fast, Secure, Reliable,

Scalable, Flexible,

More Informative

KRnet 20083

MAC:

Medium Access Control or Multi-access Control or Multiple Access Control

Protocols coordinating the use of shared resource (“channel”)

When to transmit a data?How to transmit a data?Where to transmit a data?What to transmit?

KRnet 20084

MAC Protocol

OSI ModelLayer Function

7. Application Network process to application

6. Presentation Data representation and encryption

5. Session Interhost communication

4. Transport End-to-end connections and reliability (TCP)

3. Network Path determination and logical addressing (IP)

2. Data link Physical addressing (MAC & LLC)

1. Physical Media, signal and binary transmission

MAC Protocol (=Layer 2 Protocol)

Ethernet (CSMA/CD), Token Ring, Frame Relay

Aloha, CSMA/CA(WiFi, IEEE 802.11 ), CDMA (EV-DO),TDMA (HSDPA),OFDMA (WiMax, IEEE802.16)……..

Wired (유선)

Wireless (무선)

MAC:

KRnet 20085

MAC Protocol

Half-duplex operationTime varying channel

• Reflection, diffraction, scattering

Burst channel errors• Bit-error rate can be as high as

10-3 or higher

• Packet loss can be minimized by using smaller packets, forward error correcting codes and retransmission methods such as acknowledgement packets

KRnet 20086

Why is MAC important over wireless?

Full-duplex operationStable Channel Condition

Small channel errors• Bit-error rate can be as

small as 10-6

VS.

“Wired”

“Wireless”

Tactical Data Link

Link-4TADIL-C

Link-11TADIL-A

Link-11BTADIL-B

Link-14 Link-16TADIL-J

Link-22

Frequency UHF HF/UHF VHF, Wired HF/VHF/UHF UHF HF, UHF

Data Rate 5Kbps1364, 2250, 1800

bps1200, 2400, 3600,

4800 bps110~600 bps

28.8~115.2K bps

12.7 Kbps

LOS Expansion No HF OnlyHF/SATCOM

OnlyYes (Relay) HF Only

Voice Encryption

No No No No Yes

Network Flexibility

No No No No Yes

Half-Duplex, Simplex

Half-Duplex Full-Duplex Simplex Half-Duplex Half-Duplex

Frequency HoppingNot Completed

Tactical data links involve transmissions of bit-oriented digital information which are exchanged via data links known as TacticalDigital Information Links (TADIL) used in Military communications.

KRnet 20087

TADIL : US designationsLINK: NATO designations

PHY Layer

Data rate: 2.25Kbps, 1.364KbpsHF or UHFHalf DuplexMulti-Tone-based PHY frame structure

• Preamble: 2 tones• Data: 15 Tones• One frame= 30 bits (=15data tones * 2bits(Qpsk))• Frame Structure:

Link-11 (TADIL A)

KRnet 20088

Link-11 (TADIL A)

MAC Layer

Polling-based protocol (Roll Call)Nodes sends their data when they are polled by Network Control Station (NCS) (Call-Up Message)All nodes receives the data from the pooled nodePolling sequence is round-robinWhen all nodes transmit, the cycle is repeated

KRnet 20089

Link-16 (or TADIL-J)

PHY

Data Rate28.8Kbps, 57.6Kbps, 115.2 Kbps, 238Kbps

UHF (950MHz~1150MHz)

TDMA-based MAC

Frequency Hopping• 51 Frequencies (3MHz) available

• Within a time slot

• Hopping in every 13us (every pulse)

• 128 possible pseudo-random sequences

5-data bits per a slot

KRnet 200810

Link-16 (or TADIL-J)

MACTDMA-based MAC

- Time slot: 7.8125ms- 98304 time slots (12-min 48-sec)- Time slots are organized into interleaved sets called A,

B, and C

Time Slot Allocation1. Dedicated Access • Reservation-based channel access All nodes are pre-

assigned set of time slots to transmitter and receive2. Contention Access3. Time Slot Reallocation

Stacked Net • Simultaneous communications possible

• Each Net is assigned with unique hopping pattern

KRnet 200811

Link-16 (or TADIL-J)

Nodelessness• NCS in Link-11 goes down Network goes down• No central control node• Time slot is preassigned.

Network Participant Group (NPG)• Functional Groups (Network Management, Surveillance,

Weapons Coordination, Voice Group, Fighter-to-Fighter ….)

• Group-Call-based communications

Voice Communication over Link-16• Two channels for digitized voice

communications• 16Kbps• Push-to-Talk protocol• No-Error Correction Coding, but Encryption

Relay

KRnet 200812

Link-22 (or TADIL-F)

Standardization is still on progress.

Replacement of Link-11, Interoperation with Link-16

Characteristics

HF (3-30 MHz) and/or UHF (225-400 MHz) bands

Data Rate: 4.053 Kbps (with HF), 12.667 Kbps (with UHF)

TDMA

Pre-assigned Time-slot or Dynamic Time-slot reallocation

Interrupt Time-Slot: Transmission priority

Use of Acknowledgement & Multiple Transmission Reliability

Fixed Frequency or Frequency HoppingPropagation Range: 300 nmi with HF

KRnet 200813

Two-Way Radio

Push-to-Talk (PTT), Land Mobile Radio (LMR), Personal Mobile Radio (PMR)

Standard: TETRA (ETSI), APCO (North America), Military Tactical Radio (MIL-STD-188-220)

KRnet 200814

TETRA (Release 1)• Voice +Data• IP packet data• Instant group communication• Fast call set-up time

(500ms for group-call, 250ms for single-call)• Direct Mode (DMO)

(Two-Hop Comm., Dual Watch)• Speech Codec• Over The Air Rekeying • Short Data Service (SDS)

TETRA (Release 2)• Enhanced Data

• Interworking with GSM/GPRS/UMTS

• High Speed Data (up to 384Kbps)

- TETRA Advanced Packet Service (TAPS)

- TETRA Enhanced Data Service (TEDS)

TETRA

Eight-25kHz channels / 200kHz band4:1 TDMA 4 channels (Slots) per 25 kHz carrierTotal 32 communications channels Time slot duration: 510 bits (255 symbols)Data or Voice calls can use up to 4 channelsVoice and Data can be transmitted simultaneously

Four user channels multiplexedinto one 25 kHz carrier

SPECTRUMEFFICIENCY

4 channels1 2

3 4

36 kbits/sgross bitrate

Carrier

KRnet 200815

Notable Characteristic of Tactical Communications (Link-11, Link-16, Two-way Radio)

“Group-Call” or “Multicast”-based Communication

KRnet 200816

Wireless Multicast

Wireless Multicast

Multicast over the wired backboneExtensive Researches at Layer 3 and 4: CBT, PIM-DM, PIM-SM, MBGP ……

No packet error considered Reliable and No ARQ required

Multicast over the wirelessLayer 2 Protocol >> Layer 3 and 4 Protocols

Error-prone wireless channel

Poor Reliability

KRnet 200817

ARQ required !

Increase overheads (due to ACK, RTS/CTS in Ad-Hoc), and delays as the number of member increase. Poor throughput efficiency

Lack of retransmission policy (how, when, how many times to retransmit.)

Tradeoff between reliability, throughput and delay

Reliability

Group Call Operation over APCO P-25 system (PMR)

What about Group-Call over Distributed environment?

Wireless MulticastTwo-Way Radio

No ARQ, No Retransmission

KRnet 200818

Wireless Multicast over Mesh-based Mission Critical NetworksAchieve High Data Rate by adopting WLAN technologies

Multicast Mesh Scalable Routing protocol

Wireless MulticastBroadband Mission Critical

What about Multicast in IEEE 802.11 standard?

KRnet 200819

Wireless Multicast in 802.11-based MANET No ARQNo RetransmissionMulticast right after Beacon frame: All stations have to be in wakeLowest data rate

Wireless MulticastIEEE802.11x

Not Reliable & Slow !!

PC

KRnet 200820

What about recent researches on distributed wireless networks?

Multicast Data

Beacon

Multicast Data

Beacon

M-RTS

L-CTS

M-DataSender

Leader

Receiver 1

Receiver N

SIFS SIFS

NAV

●

●

●

●

SIFS

L-ACK

M-Data NACK

Deliberate Collision

Retransmission

Legacy Solutions for Leader-Based Multicasting Protocol• Leader Based Multicasting, i.e. Leader is station which produces ACK

• Sequential ACK-based Multicasting

M-RTS

L-CTS

M-DataSender

Leader

Receiver 1

Receiver N

SIFS SIFS

NAV

●

●

●

●

SIFS

M-Data NACK

RetransmissionSIFS

ACK

ACK

Wireless MulticastAd-Hoc Researches

What if both RTS and Data are not received?

Too Much Overheads

False Report

What about wireless multicast on 4G standards?KRnet 200821

Wireless Multicast over EV-DO (EBCMCS) and WiMax (MBS)

No ARQ is applicable. Single Frequency Network (SFN) Transmissions- Same Time, Same Frequency over multi cells- Spatial Diversity- WiMax: Multi-BS Access (MBS Zone)

EBCMCS: Forward Error Correction (FEC) (Reed-Solomon code) in MAC

Wireless MulticastCellular

MBS-Zone 3MBS-Zone 2MBS-Zone 1

KRnet 200822

Conclusion

KRnet 200823

For reliable wireless multicast in tactical communications

Method to reduce overhead (multiple RTS/CTS/ACK)Optimal Data Rate SelectionRetransmission StrategyCooperate with Power Save Mode.

Voice oriented traffics

Low Data Rate

Analog Signal

Infrastructure-based

Architecture

Line-of-Sight Communication

Multimedia Traffic

(Voice, Data, Image, Video)

Broad bandwidth

Digitized Signal

Ad-Hoc-based Architecture

NLOS Communication with Multi-Hop

Fast, Secure, Reliable,

Scalable, Flexible,

More Informative

““QoS GuaranteeQoS Guarantee””““Reliable CommunicationReliable Communication”” ““Wireless SecurityWireless Security””

For MAC Protocols over Future Tactical Communications

““InteroperabilityInteroperability””