WO2013105085A1

WO2013105085A1 - A mobile ad-hoc network with reduced guard-time

Info

Publication number: WO2013105085A1
Application number: PCT/IL2013/050008
Authority: WO
Inventors: Michal Wermuth; Yoav WERMUTH
Original assignee: Rafael Advanced Defense Systems Ltd.
Priority date: 2012-01-12
Filing date: 2013-01-03
Publication date: 2013-07-18
Also published as: IN2014KN01372A; BR112014016794B1; BR112014016794A8; KR20140116189A; BR112014016794A2; KR102141458B1; IL217506A0; IL217506A

Abstract

The present invention is directed to a method for reducing the guard time of a Mobile ad-hoc networking (MANET) system during reception, according to which a transceiver architecture that is provided at each node, includes a combination of a hopping transmitter and a plurality of hopping narrowband independent receivers that are capable of receiving and processing the entire operational band assigned to the system, at once, and that include channel frequencies, dynamically selected within a wide operating bandwidth. Alternatively, the transceiver architecture includes a non-hopping wideband receiver capable of receiving and processing the entire operational band assigned to the system, at once. Several channels, arbitrarily spread over a frequency band assigned to the system are simultaneously received, while keeping the architecture of the MANET system. The transmission hopping patterns are determined to use the least possible number of frequencies. For each transmitting node, time slots in which a counterpart receiver at each remaining active node is not transmitting and a frequency channel in which no other active node transmits are found. The transmission frequency is then determined and if no other node had chosen the same time slot, and if the transceiver is not transmitting in the slot, the transmission is received, while allowing relay nodes to transmit simultaneously, using different channels. Whenever a plurality of narrowband independent receivers is used for reception, guard time is allocated to time slots on demand. Otherwise, no guard time is allocated to the time slots.

Description

A MOBILE AD-HOC NETWORK WITH REDUCED GUARD-TIME

Field of the Invention

The present invention relates to the field of mobile communication. More particularly, the invention relates to a system and method for improving the spectral efficiency and scalability of mobile ad-hoc networks.

Background of the Invention

Mobile Ad-hoc NETworks (MANETs) are self-formed and self-healing wireless networks that support data and/or voice communication between mobile or stationary nodes without any physical infrastructure.

A MANET is a type of "Mesh Network", with added mobility capabilities. In Mesh Networking, each node in the network may act as an independent router, regardless of whether or not it is connected to another network. It provides continuous connections and reconfiguration around broken or blocked paths by "hopping" from a node to another node, until the destination is reached. Fig. 1 (prior art) shows an exemplary connection path between node "A" and node "B" in a typical Mesh network.

Mesh networks are self-healing: the network can still operate when one node breaks down or when the quality of a connection is low. MANET is a mesh network, capable of dealing with the problems introduced by the mobility of the nodes. One of the drawbacks of Mesh networks is that if several subscribers need to hop through the same node, this creates a "bottleneck" at that node, and the data rate of the contending subscribers is substantially reduced.

Each mobile node manages dynamic routing tables that track the MANET topology. The routing tables may be established by running any routing protocol suitable for MANETs, for example Optimized Link State Routing protocol (OLSR - an IP routing protocol optimized for mobile ad-hoc networks) or Ad hoc On-Demand Distance Vector routing protocol (AODV - a routing protocol for mobile ad hoc networks). OLSR is a proactive Link State (LS) algorithm that holds the radio link status information, and AODV is a reactive Distance Vector (DV) algorithm that holds only the distances to all the other nodes. The topology may possibly include additional parameters, such as link quality, physical location and channel frequency.

MANETs can be used either in military environment, or in areas where the existing infrastructure collapsed (e.g., disaster areas) or is not sufficient. In the recent years, there has been a growing need for wideband MANET capabilities to support more users (nodes) and more demanding applications. However, the spectrum resource is scarce, and the current MANET algorithms do not exploit the spectrum efficiently enough, in order to meet the growing needs.

The MANET nodes are identified by a node ID and run a distributed Medium Access Control (MAC) algorithm that allocates time resources to nodes in every MANET channel. The system utilizes a limited number of radio channels, while managing every channel separately, and dividing the timeline of each channel between the MANET nodes. If the timeline is divided to slots (as shown in Fig. 2), the time division between MANET nodes is called "TDMA", namely Time Division Multiple Access (a channel access method for shared medium networks that allows several users to share the same frequency channel by dividing the signal into different time slots).

In wireless MANET networks, sophisticated distributed algorithms are needed to manage the access to several radio channels, determining for every node when to receive and when to transmit in any channel, for each time period.

In a standard MANET setting (where the transceiver can receive only one channel at a time), once the channel frequency has been set, the mesh networking is carried on only among the subscribers that are tuned to that channel, and the MAC algorithm has meaning only within the selected channel, and is blind to all other channels. Although the channel frequency can be selected among many frequencies, once it has been chosen, it becomes unrelated to the networking operation. Thus, a MANET system with a collection of channels, is in fact a collection of unconnected parallel MANET systems, each one working on its own channel only, with data rate and reliability performance limited by the width of one single channel. This observation is also true when the timeline is divided in time slots: during every time slot, in every channel, a different MANET is managed, and the participants of that MANET run distributed algorithms to decide how to divide the channel between them (i.e., to determine which node will transmit at what time). Therefore, whenever a hopping receiver is used, a "guard time" (the maximal propagation delay which can occur in the system) is used as a safety margin before the receiver is allowed to hop to the next frequency. However, this guard time adds up idle periods to the time slot, thus slowing down the TDMA cycle and impairing the time-efficiency of the system.

It is therefore an object of the present invention, to improve the spectral efficiency and scalability of MANET systems, while reducing the guard-time allocated to time slots.

It is yet another object of the present invention to provide an improved MANET system that is being capable of reducing latency (the amount of time it takes a packet of data to move across a network connection).

Other objects and advantages of the invention will become apparent as the description proceeds.

Summary of the Invention

The present invention is directed to a method for reducing the guard time of a Mobile ad-hoc networking (MANET) system during reception, according to which a transceiver architecture that is provided at each node, includes a combination of a hopping transmitter and a plurality of hopping narrowband independent receivers that are capable of receiving and processing the entire operational band assigned to the system, at once, and that include channel frequencies, dynamically selected within a wide operating bandwidth. Alternatively, the transceiver architecture includes a non-hopping wideband receiver capable of receiving and processing the entire operational band assigned to the system, at once.

Several channels, arbitrarily spread over a frequency band assigned to the system are simultaneously received, while keeping the architecture of the MANET system. The transmission hopping patterns are determined to use the least possible number of frequencies. For each transmitting node, time slots in which a counterpart receiver at each remaining active node is not transmitting and a frequency channel in which no other active node transmits are found. The transmission frequency is then determined and if no other node had chosen the same time slot, and if the transceiver is not transmitting in the slot, the transmission is received, while allowing relay nodes to transmit simultaneously, using different channels. Whenever a plurality of narrowband independent receivers are used for reception, guard time is allocated to time slots on demand. Otherwise, no guard time is allocated to the time slots.

According to one embodiment, the wideband receiver receives several channels simultaneously and includes:

a) a global band preselector for selecting a frequency range;

b) a global Low Noise Amplifier for amplifying the selected range;

c) a global gain control unit, for controlling the global gain of the reference receiver;

d) an anti-aliasing filter for filtering the amplified signals;

e) one or more Analog to Digital Converters (ADCs) for sampling the received signal;

f) an ADC driver for controlling the operation of the ADCs;

g) a control unit for controlling the gain of the global gain control unit; and h) a digital signal processing unit for processing at once, samples from the RF band. Nodes may receive and transmit by using full-duplex or half-duplex transceivers.

The guard time may be allocated on demand by:

a) ordering all RF channels sequentially indexing them according to a hopping pattern;

b) allowing a receiver to hop over even-indexed frequencies and to remain on each frequency for a time period equal to one time slot plus the maximal propagation delay difference that can occur between any two nodes; and c) allowing another receiver to hop over odd-indexed frequencies and to remain on each frequency for a time period equal to one time slot plus the maximal propagation delay difference that can occur between any two nodes.

Optionally, no guard-time is allocated to time slots.

Whenever a conventional receiver with two or more independent simultaneous receive channels is used, the guard-time allocated to time slots is reduced by: a) ordering all RF channels are by sequentially indexing according to the hopping pattern;

b) allowing a first receiver to hop over even-indexed frequencies and to remain on each frequency for a time period equal to one time slot plus the maximal propagation delay difference that can occur between any two nodes; and c) allowing a second receiver, staggered in time by one time slot relative to the first receiver, to hop over odd-indexed frequencies and to remain on each frequency for a time period equal to one time slot plus the maximal propagation delay difference that can occur between any two nodes.

Whenever the duration of the maximal possible propagation delay difference is more than the length of one time slot, the guard time may be omitted by using more than two receivers. Whenever a single wideband receiver is used, the guard time may be omitted without channel indexing or receiver time slot synchronization.

The guard time may be reduced with more than one frequency hop per time slot or with maximal delay shorter than the frequency hop period.

The present invention is directed to a Mobile Ad-Hoc Networking (MANET) system with a reduced guard time during reception, which comprises:

a. a transceiver architecture provided at each node, which includes a combination of a hopping transmitter, and

a.l) a plurality of hopping narrowband independent receivers that are being capable of receiving and processing the entire operational band assigned to the system, at once, and that include channel frequencies, dynamically selected within a wide operating bandwidth, or

a.2) a non-hopping wideband receiver being capable of receiving and processing the entire operational band assigned to the system, at once;

wherein the MANET system is adapted to:

b. simultaneously receive several channels, arbitrarily spread over a frequency band assigned to the system, while keeping its architecture; c. determine transmission hopping patterns to use the least possible number of frequencies;

d. for each transmitting node, find time slots, in which a counterpart receiver at each remaining active node is not transmitting and a frequency channel in which no other active node transmits;

e. for each transmitting node, determine transmission frequency; and f. for each transmitting node, if no other node had chosen the same time slot, and if the transceiver is not transmitting in the slot, receive the transmission, while allowing relay nodes to transmit simultaneously, using different channels; g. allocate guard time to time slots on demand or otherwise, allocate no guard time to the time slots such that, whenever a plurality of narrowband independent receivers are used for reception.

Brief Description of the Drawings

In the drawings:

Fig. 1 (prior art) shows a conventional typical mesh connection;

Fig. 2 (prior art) shows a typical TDMA cycle;

Fig. 3a is a block diagram of a reference receiver with two independent receiving channels, according to an embodiment of the invention;

Fig. 3b illustrates a block diagram of an expanded version with four independent receive channels, according to an embodiment of the invention;

Fig. 3c illustrates a block diagram of a reference receiver, according to an embodiment of the invention;

Fig. 4 is a block diagram of a wideband reference transmitter, according to an embodiment of the invention;

Fig. 5 (prior art) illustrates a possible near-far nodes displacement in a MANET system, where a node is close to one node, but is far from another node;

Fig. 6a (prior art) shows a specific case of the MANET of Fig. 6, in which the fixed guard time allocation consumes 50% of the cycle time;

Fig. 6b shows a specific case of the MANET of Fig. 5, with no guard time according to an embodiment of the invention; and

Fig. 6c shows an embodiment of the invention, implemented using the improved MANET transceiver architecture;

Detailed Description of the Invention

The improved MANET system proposed by the present invention uses a wideband receiver, along with sophisticated signal processing, in order to take advantage of the simultaneous reception of several channels, arbitrarily spread over a wideband frequency range, while remaining within the context of MANET architecture. The transceiver architecture of the improved MANET system includes an independent transmitter which may operate on predetermined fixed channels, or may be hopping according to some hopping sequence and rate.

A spectrum - efficient MANET with increased time efficiency and reduced latency uses simultaneous reception and comprises a reference receiver and a reference transmitter.

Prior art reference receiver

For the purpose of illustrating the basic implementations of the improved MANET algorithms, either a two-receiver reference configuration or a four- receiver reference configuration is chosen as the reference receiver.

Fig. 3a illustrates a block diagram of a prior art reference receiver with two independent receiving channels. Solid lines indicate radio-frequency (RF) paths, and dashed lines indicate control paths. The receiver architecture includes at least two independent receiving paths, each one providing an individually programmable receiving channel. The reference receiver 30 comprises a global band preselector 31, which selects the range and forwards it to a global Low Noise Amplifier (LNA) 32 for amplification. The global range is split into sub- bands by means of programmable preselector filters 33a and 33b. The Local Oscillator (LO) signals, feeding the mixers 34a and 34b at variable frequencies and / (for the two channel version, as shown in Fig. 3a) or fi ^*2, fz and ₄ (for the four channel version, as shown in Fig. 3b), are generated by independent synthesizers 35a and 35b, each programmed by the control unit 36. The LO signals, the sub-band ranges, and the gain control levels, are dynamically determined by the digital control unit 36, according to the receive method employed, and the frequency and strength of the desired receive channels. The outputs of the mixers are at a common low intermediate frequency (IF), and are connected to the signal processing unit 37, usually of the FPGA type (due to the high processing speed required), which carries out signal sampling (at IF frequency) and digital processing of all channels simultaneously.

Multi-channel receivers up to four independent channels have already been made available commercially. For instance, Rockwell-Collins offers the "FlexNet-Four", which includes up to four receivers, independently programmable over the HF/VHF/UHF bands (2 ÷ 2000 MHz), and IAI/ELTA offers the "ARC-840D", which comes in two-receiver and four-receiver configuration, independently programmable over the VHF UHF bands (30 ÷ 1220 MHz). Thus, receiver architectures with up to four independent receivers are of proven feasibility. More independent channels may be readily added by replicating the parallel branches.

Fig. 3b illustrates a block diagram of an expanded version (of Fig. 3a) with four independent receive channels. Solid lines indicate radio-frequency (RF) paths, and dashed lines indicate control paths. Since the hardware complexity is fast- growing, more than four channels may become less practical. A similar array may be picked-up by any person skilled in the art.

Improved MANET reference receiver

Fig. 3c illustrates a block diagram of a reference receiver, according to an embodiment of the invention. Solid lines indicate RF paths, the dashed line indicates control path, and the wide arrow indicates a data bus. Using, for example, the 225-400 MHz UHF band which is normally allocated to airborne communication, it is possible to construct receivers which can simultaneously receive the whole band with sufficient dynamic range. The technologies that enable such receivers are (1) Analog to Digital Converters (ADC) which perform direct signal sampling at Radio Frequency (RF), and practically set the limit for the system's bandwidth and dynamic range, (2) the Digital Signal Processing section, which processes the whole RF band at once, and is usually implemented using Field Programmable Gate Arrays (FPGA) when dealing with high bandwidth systems. Such receiver architecture is currently viable for many systems. Digital processing power is now sufficient for nearly all applications, as well as ADC technology, which is sufficient for most systems that require the highest possible dynamic range. An example of a modern ADC that can be used in the implementation of the wideband reference radio receiver is the ADC 12D 1800 by National semiconductors, a dual channel ADC with a maximum sampling frequency of 1800 MHz on each of the channels. This device is specifically targeting wideband software defined radios. Thus, unlike a prior art receiver that receives only few channel at once, by splitting the band into sub-band and sequentially reprogramming the frequency of the channels, the reference receiver processes the whole band at once, i.e., receives all the channels simultaneously.

Reference transmitter

Fig. 4 illustrates a block diagram of a reference transmitter capable to operate in both wideband and frequency-hopping modes, according to an embodiment of the invention. Solid lines indicate RF paths, the dashed line indicates control path, and the wide arrow indicates a data bus. This transmitter architecture is the most likely to be selected for wideband applications by a person skilled in the art. The samples of the modulated signal, right at final frequency, are mathematically generated by the signal processing unit in a digital form, and converted to analog form by means of a high-speed DAC (Digital to Analog Converter) such as the AD9739A (Analog Devices), which is capable to operate at a rate up to 2.5 Giga-Samples/Second. The signal samples out of the DAC are transformed to analog form by a global-band reconstruction filter, and pre- amplified by a low-level RF amplifier. Then the signal is fed to a power-control attenuator, whose attenuation level is dynamically controlled by the control unit. A global-band filter at the attenuator output cleans-up far-out distortion products generated by the pre-amplifier. The filter output is fed to an RF Driver, which amplifies it to a level sufficient to drive the final PA (Power Amplifier) to the maximal allowed transmit power. The output from the PA passes through a global-band Harmonic Filter, which cleans-up the PA products at multiples of the transmit frequency, and then the signal reaches the transmit antenna.

Improving the spectrum-efficiency of a MANET

The present invention proposes a new method of MANET implementation that uses the spectrum more efficiently than in prior-art, and provides higher data rates and shorter latency than existing MANET implementation methods do. The improved MANET system proposed by the present invention exploits the capability of the reference receiver to simultaneously receive the whole frequency range (when the improved MANET reference receiver is employed) or several channels over a wideband frequency range (using a prior-art reference receiver), while in the context of a MANET architecture.

Practical feasibility:

The improved MANET algorithms proposed by the present invention use half- duplex transceivers. Half-duplex transceivers are flexible and easy to implement, as one is concerned only with protecting the receiver from burning- out during transmission. In one possible implementation, this protection can be easily and inexpensively achieved by means of a simple unit known as "antenna switch", which is capable to operate correctly regardless of the operating frequency.

Using improved MANET to increase time - efficiency of conventional MANETs In conventional MANET systems, the relative physical distance between every two nodes is the outcome of operational requirements in the field. Usually, the above distances are not known a-priori, they have random lengths and may be very different from each other. For instance, in the MANET system shown in Fig. 5, node D is close to node B, but far from node A. The time delay, due to electromagnetic wave propagation from node A to node D is d. If both nodes B and A wish to transmit to node D, the propagation time of the transmission from A to D will be longer than the propagation time of the transmission from B to D. Since according to conventional TDMA scheme, node D is listening during fixed-length time slots to receive each node in the system, if the transmission of node A arrives with delay, part of the data packet, or even the whole data packet, will be lost. This happens because node D will switch to the frequency of another node before all the data from node A reached it. The same happens also in frequency-hopping mode, where the nodes hop through several frequencies during a single TDMA time slot, because node D will hop to a new frequency before the all transmission from A on the current frequency hop has reached its destination. In order to overcome this problem, in prior art frequency-hopping/TDMA schemes, at the end of every time slot (no matter if there is only one frequency hop in that time slot or more than one), the physical layer pre-allocates a "guard time" equal to the maximal propagation delay which can occur in the system, so that both short-delayed and long-delayed transmissions can reach their destination before the receiver is allowed to hop to the next frequency. This guard time adds up idle periods to the time slot, thus slowing down the TDMA cycle and impairing the time-efficiency of the system.

According to an embodiment of the invention, the system allows omitting the guard time pre-allocated in the physical layer and instead, allocating it on demand. This embodiment can be implemented in any prior-art receiver with two or more independent simultaneous receive channels as follows: If all RF channels are ordered by sequentially indexing them according to the hopping pattern, receiver #1 hops over even-indexed frequencies, and remains on each frequency for a time period equal to one time slot plus the maximal propagation delay difference that can occur between any two nodes. Receiver #2 does exactly the same, except that it hops over odd-indexed frequencies, and it is staggered in time by one time slot relative to receiver #1. With this arrangement, it can be easily appreciated from the example in Fig. 6b, that both close-in transmitters with short delay, and far-out transmitters, with long delay, are received correctly by either one of the receivers.

It can be easily appreciated, however, that if the duration of the maximal possible propagation delay difference is more than the length of one time slot, then more than two receivers will be required in order to omit the guard time using prior-art receivers. Moreover, even the basic two-receiver configuration adds considerable hardware and software complexity. The above difficulty is overcome by using the improved MANET receiver architecture, which, with a proper method, allows omitting the guard time using one single receiver and a low-complexity algorithm, as described below.

Fig. 6c shows an embodiment of the invention, implemented using the improved MANET transceiver architecture. Here there are no restrictions to the delay length, since the receiver is "watching" at all channels simultaneously, thus it will always be ready, no matter what the delay length is, and, as opposed to the implementation with a prior-art transceiver, there is no need for channel indexing or receiver time slot synchronization, which substantially reduces both hardware and software complexity. Moreover, the receiver does not need to know the frequency hopping sequences of the transmitters.

The omission of the fixed guard time significantly improves the time utilization. Figs. 6a , 6b and 6c show a specific case of the MANET of Fig. 5, in which there is only one frequency hop in each transmission and the maximal propagation delay length d (that corresponds to the physical distance), is equal to a period of a single time slot. In Fig. 6a, the fixed guard time allocation consumes 50% of the cycle time. The time-efficiency improvement due to the omission of the guard time in Fig. 6b and 6c is significant. The guard time can also be saved in other TDMA schemes, with more than one frequency hop per time slot and/or with maximal delay shorter than the frequency hop period. Since improved MANET operates in half-duplex mode, upon switching from receiving state to transmitting state, all the receiving paths become disconnected. Thus a Forward Error Correction (FEC) code is introduced in order to compensate for the possible loss of the "tail" of the last receiving time slot before reaching the transmission state. However, since usually the improved MANET system stays in receive mode for many time slots before switching to transmission mode, the FEC will be required to correct only a small percentage of the total data block. Thus the FEC rate can be made high, and the net data bit rate is not appreciably reduced.

The above examples and description have of course been provided only for the purpose of illustration, and are not intended to limit the invention in any way. As will be appreciated by the skilled person, the invention can be carried out in a great variety of ways, employing more than one technique from those described above, all without exceeding the scope of the invention.

Claims

1. A method for reducing the guard time of a Mobile Ad-Hoc Networking (MANET) system during reception, comprising:

a) at each node, providing a transceiver architecture that includes a combination of a hopping transmitter, and

a.l) a plurality of hopping narrowband independent receivers that are being capable of receiving and processing the entire operational band assigned to said system, at once, and that include channel frequencies, dynamically selected within a wide operating bandwidth, or

a.2) a non-hopping wideband receiver being capable of receiving and processing the entire operational band assigned to said system, at once;

b) simultaneously receiving at least several channels, arbitrarily spread over a frequency band assigned to said system, while keeping the architecture of said MANET system;

c) determining transmission hopping patterns to use the least possible number of frequencies;

for each transmitting node

d) finding time slots, in which a counterpart receiver at each remaining active node is not transmitting and a frequency channel in which no other active node transmits;

e) determining transmission frequency; and

f) if no other node had chosen the same time slot, and if the transceiver is not transmitting in said slot, receiving the transmission, while allowing relay nodes to transmit simultaneously, using different channels, wherein, whenever a plurality of narrowband independent receivers are used for reception, allocating guard time to time slots on demand, otherwise, allocating no guard time to said time slots.

2. A method according to claim 1, wherein the wideband receiver receives several channels simultaneously and includes: a) a global band preselector for selecting a frequency range;

b) a global Low Noise Amplifier for amplifying the selected range;

c) a global gain control unit, for controlling the global gain of said reference receiver;

d) an anti-aliasing filter for filtering the amplified signals;

f) an ADC driver for controlling the operation of said ADCs;

g) a control unit for controlling the gain of said global gain control unit; and h) a digital signal processing unit for processing at once, samples from the RF band.

3. A method according to claim 1, wherein nodes receive and transmit by using full- duplex or half-duplex transceivers.

4. A method according to claim 1, wherein the guard time is allocated on demand by: a) ordering all RF channels sequentially indexing them according to a hopping pattern;

5. A method according to claim 1, wherein no guard-time is allocated to time slots.

6. A method according to claim 1, wherein whenever a conventional receiver with two or more independent simultaneous receive channels is used, the guard-time allocated to time slots is reduced by:

a) ordering all RF channels are by sequentially indexing according to the hopping pattern; b) allowing a first receiver to hop over even-indexed frequencies and to remain on each frequency for a time period equal to one time slot plus the maximal propagation delay difference that can occur between any two nodes; and c) allowing a second receiver, staggered in time by one time slot relative to said first receiver, to hop over odd-indexed frequencies and to remain on each frequency for a time period equal to one time slot plus the maximal propagation delay difference that can occur between any two nodes.

7. A method according to claim 1, wherein whenever the duration of the maximal possible propagation delay difference is more than the length of one time slot, the guard time is omitted by using more than two receivers.

8. A method according to claim 1, wherein whenever a single wideband receiver is used, the guard time is omitted without channel indexing or receiver time slot synchronization.

9. A method according to claim 1, wherein the guard time is reduced with more than one frequency hop per time slot.

10. A method according to claim 1, wherein the guard time is reduced with maximal delay shorter than the frequency hop period.

11. A Mobile Ad-Hoc Networking (MANET) system with a reduced guard time during reception, comprising:

a.l) a plurality of hopping narrowband independent receivers that are being capable of receiving and processing the entire operational band assigned to said system, at once, and that include channel frequencies, dynamically selected within a wide operating bandwidth, or a.2) a non-hopping wideband receiver being capable of receiving and processing the entire operational band assigned to said system, at once;

wherein said MANET system is adapted to:

b. simultaneously receive several channels, arbitrarily spread over a frequency band assigned to said system, while keeping its architecture; c. determine transmission hopping patterns to use the least possible number of frequencies;

d. for each transmitting node, find time slots, in which a counterpart receiver at each remaining active node is not transmitting and a frequency channel in which no other active node transmits; e. for each transmitting node, determine transmission frequency; and f. for each transmitting node, if no other node had chosen the same time slot, and if the transceiver is not transmitting in said slot, receive the transmission, while allowing relay nodes to transmit simultaneously, using different channels;

g. allocate guard time to time slots on demand or otherwise, allocate no guard time to said time slots such that, whenever a plurality of narrowband independent receivers are used for reception.