determination of the topology of high survival hf radio communication network andrea abrardo

DETERMINATION OF THE TOPOLOGY OF HIGH SURVIVAL HF RADIO COMMUNICATION NETWORK

Andrea Abrardo.

Outline

2SWING Final Meeting | CNIT - Pisa, Italy13/12/2013

1. Communications requirements2. The physical topology of connections

envisaged in the SWING project3. Higher layer requirements4. Identification of MAC techniques and

possible scenarios5. Comparisons6. Looking forward

Communications requirements

• ECIs send data only to their home CGAs (ECIs to ECIs communication is not required, not even within the same area).

• More than one ECI belonging to the same area, i.e., connected to the same CGA, may transmit at same time.

• Communication between different CGAs must be permitted.

• The major part of network traffic is confined within each area, i.e., ECIs to CGAs communications.

• Accordingly, the probability of concurrent transmissions of ECIs (either belonging to the same area or not) is greater than that of CGAs.


HYBRID TREE/MESH TOPOLOGY


The choice of the topology has a direct impact on the design of higher layer protocols, and vice versa.

Higher layers requirements

• SWING requirements involving higher layer operations– Most of the times end-to-end communications are

confined to single-hop communications, i.e., from ECIs to CGAs or among CGAs (MAC layer aspects)

• Considering these premises we provided:– MAC requirements– Identification of possible MAC techniques suitable for

the SWING system– MAC protocols comparison


MAC requirements

• Contention-based MAC protocols such as IEEE 802.11 provide fast and efficient channel access in presence of light traffic.

• Contention-free protocols such as IEEE 802.4 (token bus) achieve high efficiency under heavy loads, and provide bounded access time as well.

• One of the factors that influence the performance of MAC protocols for HF networks is the link turnaround time, i.e., the time it takes for a node to process a received packet and to send back a response.


Identification of possible MAC techniques: Token Passing

• Token passing is a contention-free protocol where the nodes agree that only the node that currently holds a token is allowed to transmit.

• The HF Token Protocol (HFTP) is a token bus protocol, so each node can (nominally) send data directly to any or all other nodes (broadcast channel).

• Token passing is attractive for use in surface-wave naval high-frequency (HF) radio networks due to its potential for high throughput, fairness, and bounded access time.


Identification of possible MAC techniques: Distributed Coordination for High Frequency (DCHF)

• DCHF is a contention-based scheme based on the popular wireless MAC protocol IEEE 802.11 DCF.

• The main characteristics of DCHF are the lack of synchronization requirement and the possibility left to the nodes to join or leave the network, without any management overhead.

• DCHF uses only "virtual carrier sensing“ implemented through the exchange of RTS and CTS packets.


Possible scenarios

Considering the general comms requirements, and the characteristics of the two MAC schemes we propose 3 different solutions based on 3 different scenarios:

1. Token passing scenario: in this solution the logical ring is passed among all the nodes of the SWING network (both among ECIs and among CGAs).

2. Contention based scenario: all nodes belonging to SWING network apply DCHF MAC technique; every transmitting node senses the channel and then establishes a connection with the receiver.

3. Mixed scenario: in this case, we have a contention free access technique (i.e., HFTP) for inter-area communications, i.e., between ECIs and their home CGA, while for the global network (communication between CGAs) we consider a contention based access technique (i.e. DCHF).


Token Passing scenario

This solution allows every radio terminal to transmits its data without incurring in collisions.

In case of heavy traffic, this procedure helps regulating the access to the channel avoiding collisions.

On the other hand, for light traffic (i.e. only one ECI want to transmit to the respective CGA) this solution introduces a strong management overhead, which severely degrades the system performance.

Do not recommended in presence of long turnaround times (due to long interleavers).


Contention based Scenario

Suitable for light traffic (no collisions).

In presence of long turn around times it is necessary to avoid RTS/CTS: this is possible if each node lies in the interference region of each other (channel sensing is sufficient to avoid collisions).


Mixed Scenario

Whenever an ECI have to transmit a packet to its home CGA, it waits for the reception of the token that is continuously exchanged within the logical ring composed by one CGA and its connected ECIs.

When a CGA receives the token, it starts the contention based procedure to submit a pending packet towards another CGA. In case no pending packet is present, the token is released, otherwise it is kept until packet transmission.


Such a solution could efficiently manage the tradeoff between access time and system throughput.

Comparisons (Simulations)

Comparisons


Behavior of MAC techniques with turnaround of 1 s.

Top: average latency per packet in DCHF (red) and HFTP (blue);

Down: channel utilization in DCHF (red) and HFTP (blue).

Simulated scenario

Comparisons (Simulations)

Comparisons


Throughput versus turn around: saturation traffic analysis.

Looking forward

• Include MAC protocols in the SWING system.• Network layer issues:– In the present SWING scenario, network functionality

can be regulated as a transparent bridge, without the need of additional overhead due to IP addresses.

– However, scaling to larger networks with more complex topologies needs the introduction of routing algorithms.


determination of the topology of high survival hf radio communication network andrea abrardo

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