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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””
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