KR102141458B1 - A mobile ad-hoc network with reduced guard-time - Google Patents

Abstract

The present invention relates to a method for reducing the protection time of a mobile ad hoc networking (MANET) system, comprising a combination of a hopping transmitter and a plurality of hopping narrowband independent receivers capable of receiving and processing the entire operating band allocated to the system at one time. The transceiver architecture provided for each node, including channel frequencies that are dynamically selected within a wide operating bandwidth, follows this method. Alternatively, this transceiver architecture includes a non-hopping broadband receiver capable of receiving and processing the entire operating band allocated to the system at one time. Several channels spread randomly on the frequency band allocated to the system are simultaneously received while maintaining the architecture of the MANET system. The transmission hopping pattern is determined to use the minimum possible number of frequencies. For each transmitting node, a time slot in which the corresponding receiver in each remaining active node is not transmitting, and a frequency channel that other active nodes are not transmitting are found. Then, if the transmission frequency is determined, and the other node does not select the slot at the same time and the transceiver is not transmitting within the slot, the transmission is received, allowing relay nodes to transmit simultaneously using different channels. When multiple narrow-band independent receivers are used for reception, the guard time is allocated to the time slot upon request. Otherwise, no protection time is assigned to the time slot.

Description

Mobile ad-hoc network with reduced protection time{A MOBILE AD-HOC NETWORK WITH REDUCED GUARD-TIME}

The present invention relates to the field of mobile communications. More particularly, the present invention relates to systems and methods for improving spectral efficiency and scalability of mobile ad-hoc networks.

Mobile Ad-hoc NETworks (MANET) are self-formed and self-healing radios that support data and/or voice communication between mobile or fixed nodes without any physical infrastructure. It is a network.

MANET is a kind of "mesh network" with additional mobile capabilities. In a mesh network, each node in the network can act as an independent router regardless of whether it is connected to another network. It provides continuous concatenation and reconfiguration by bypassing broken or blocked paths by "hopping" from one node to another until it reaches its destination. FIG. 1 (prior art) shows an exemplary connection path between nodes “A” and “B” in a typical mesh network.

The mesh network is self-healing. The network can still operate when one node is disconnected or the connection quality is low. MANET is a mesh network that can solve the problems introduced by the mobility of nodes. One disadvantage of the mesh network is that when several subscribers need to hop through the same node, a "bottleneck" occurs at that node, significantly reducing the data rate of the subscribers.

Each mobile node maintains a dynamic routing table that tracks the MANET topology. This routing table can be any routing protocol suitable for MANET, such as the Optimized Link State Routing protocol (OLSR) or an ad hoc on-demand distance vector routing protocol (AODV: Ad) hoc On-Demand Distance Vector routing protocol (routing protocol for mobile ad hoc networks). OLSR is a proactive link state (LS) algorithm that holds radio link state information, and AODV is a reactive distance vector (DV) algorithm that only holds distances to all other nodes. This topology may be possible to include additional parameters such as link quality, physical location, and channel frequency.

MANET can be used in military environments, or in areas where the existing infrastructure has collapsed or is inadequate (eg, disaster areas). Recently, there is an increasing need for broadband MANET functionality to support more users (nodes) and more demanding applications. However, the spectrum resources are insufficient, and the current MANET algorithm does not utilize the spectrum efficiently enough to meet the increasing demand.

The MANET node is identified by the node ID, and executes a distributed media access control (MAC) algorithm that allocates time resources to the node for each MANET channel. The system uses a limited number of radio channels, manages each channel individually, and splits the timeline of each channel between MANET nodes. If this timeline is divided into slots (as shown in Fig. 2), the time division between MANET nodes is "TDMA", i.e., time division multiple access (by dividing the signal into different time slots, users of life span the same frequency channel). It is called a channel access method for a shared media network that enables sharing.

In a wireless MANET network, a sophisticated distributed algorithm needs to manage access to several radio channels, which determines for each node when received and transmitted within any channel during each time period.

In a standard MANET setup (where the transmitter and receiver can only receive one channel at a time), after the channel frequency is established, the mesh network runs only between subscribers tuned to that channel, and the MAC algorithm is the selected channel. It has meaning only within me, and I can't see all the other channels. The channel frequency may be selected from among multiple frequencies, but after the frequency is selected, the frequency becomes independent of the networking operation. Therefore, a MANET system with one set of channels is a collection of parallel MANET systems that are virtually unconnected, each of which operates only on its own channel, and provides data rate and reliability performance limited by the width of one single channel. Have This observation also occurs when the timeline is divided into time slots. During each time slot, within each channel, each MANET is managed, and the participants of that MANET are distributed to determine how to split the channel between them (i.e., to determine when and which node to send). Run the algorithm. Therefore, whenever a hopping receiver is used, the "guard time" (the maximum propagation delay that can occur in the system) is the safety margin before the receiver is allowed to hop to the next frequency. Is used. However, this protection time adds an idle period to the time slot, slowing down the TDMA cycle and degrading the time efficiency of the system.

Therefore, it is an object of the present invention to improve the spectral efficiency and scalability of a MANET system while reducing the protection time allocated to time slots.

Another object of the present invention is to provide an improved MANET system that can reduce latency (time taken for one data packet to travel through a network connection).

Other objects and advantages of the present invention will become apparent through the description below.

The present invention relates to a method for reducing the protection time of a mobile ad hoc networking (MANET) system during reception, comprising a combination of a hopping transmitter and a plurality of hopping narrowband independent receivers capable of receiving and processing the entire operating band allocated to the system at one time. And includes a dynamically selected channel frequency within a wide operating bandwidth, and the transceiver architecture provided for each node conforms to the above method. Alternatively, this transceiver architecture includes a non-hopping broadband receiver that can receive and process the entire operating band assigned to the system at one time.

Several channels spread randomly on the frequency band allocated to the system are simultaneously received while maintaining the architecture of the MANET system. The transmission hopping pattern is determined to use the minimum possible number of frequencies. For each transmitting node, a time slot in which a counterpart receiver in each remaining active node is not transmitting, and a frequency channel not being transmitted by another active node are found. Then, the transmission frequency is determined, and if the other node does not select the same time slot and the transceiver is not transmitting within that slot, the transmission is received, using different channels, allowing relay nodes to transmit simultaneously. When multiple narrowband independent receivers are used for reception, the guard time is allocated to the time slot when requested. If there is no request, no protection time is assigned to the time slot.

According to one embodiment, the broadband receiver simultaneously receives several channels,

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

b) a global low noise amplifier to amplify 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 signal;

e) one or more analog-to-digital converters (ADCs) for sampling the received signal;

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

g) a control unit for controlling the gain of the global gain control unit; And

h) A digital signal processing unit for processing samples from the RF band at once.

Nodes can receive and transmit using a full-duplex or half-duplex transceiver.

Protection time:

a) aligning all RF channels by sequentially indexing all RF channels according to a hopping pattern;

b) cause the receiver to hop on an even-indexed frequency and maintain each frequency for a time period equal to the sum of the maximum propagation delay differences that can occur between one time slot and any two nodes; And

c) by requesting other receivers to hop on an odd-indexed frequency and maintaining each frequency for a period of time equal to the sum of the maximum propagation delay differences that can occur between one time slot and any two nodes. Can be assigned accordingly.

Optionally, the guard time is not assigned to a time slot.

If a conventional receiver with two or more independent simultaneous receive channels is used, the protection time allocated to the time slot is:

a) aligning all RF channels by sequentially indexing all RF channels according to a hopping pattern;

b) cause the first receiver to hop on an even-indexed frequency and remain on each frequency for a period of time equal to the sum of the maximum propagation delay differences that can occur between one time slot and any two nodes; And

c) The second receiver, which is staggered in time by one time slot compared to the first receiver, causes the second receiver to hop on the frequency of the odd index, and the maximum that can occur between one time slot and any two nodes It is reduced by keeping each on a frequency for a time period equal to the sum of propagation delay differences.

If the duration of the maximum possible propagation delay difference is longer than one time slot, the guard time can be omitted using two or more receivers.

When a single broadband receiver is used, the guard time can be omitted without channel indexing or receiver time slot synchronization.

The guard time can be reduced to have one or more frequency hops per time slot or a maximum delay shorter than the frequency hop period.

The present invention relates to a mobile ad hoc networking (MANET) system with reduced protection time during reception, the system comprising:

a. A transceiver architecture provided for each node, with a hopping transmitter:

a.l) a plurality of narrowband independent receivers capable of receiving and processing the entire operating band assigned to the system at a time and including a dynamically selected channel frequency within a wide operating bandwidth, or

a.2) the transceiver architecture comprising a combination of non-hopping broadband receivers capable of receiving and processing the entire operating band allocated to the system at one time,

The MANET system is:

b. While maintaining the architecture of the MANET system, simultaneously receiving at least several channels randomly spread over a frequency band allocated to the MANET system;

c. Determine a transmission hopping pattern to use the minimum possible number of frequencies;

d. For each transmitting node, find a time slot not transmitted by the corresponding receiver at each remaining active node and a frequency channel not transmitted by the other active node;

e. For each transmitting node, determining a transmitting frequency; And

f. For each transmitting node, if another node has not selected the same time slot, and if the transceiver is not transmitting within the slot, receive a transmission and allow relay nodes to transmit simultaneously using different channels and ;

g. It is configured to allocate a guard time to a time slot when requested, and not to allocate a guard time to the time slot so that multiple narrow-band independent receivers can be used for reception whenever there is no request.

Figure 1 (prior art) shows a typical mesh connection in the prior art.
Figure 2 (Prior Art) shows a typical TDMA cycle.
3A is a block diagram of a reference receiver with two independent receive channels according to one embodiment of the present invention.
3B shows a block diagram of an extended version with four independent receive channels according to one embodiment of the present invention.
3C shows a block diagram of a reference receiver according to one embodiment of the present invention.
4 is a block diagram of a broadband reference transmitter according to an embodiment of the present invention.
FIG. 5 (prior art) shows a possible near-far node arrangement within a MANET system, where the node is close to one node and far from the other.
FIG. 6A (prior art) shows a special case of the MANET of FIG. 6 in which the fixed protection time allocation consumes 50% cycle time.
FIG. 6B shows a special case of the MANET of FIG. 5 without protection time according to one embodiment of the invention.
6C shows one embodiment of the invention implemented using an improved MANET transceiver architecture.

The improved MANET system proposed by the present invention uses a broadband receiver with sophisticated signal processing to take advantage of simultaneous reception of several channels spread randomly over a wide range of broadband frequencies while remaining within the context of the MANET architecture. do.

The transceiver architecture of the improved MANET system includes an independent transmitter that can operate on a predetermined fixed channel, or can hop according to several hopping sequences and rates.

Spectrum-efficient MANET with improved time efficiency and reduced latency uses simultaneous reception and includes a reference receiver and a reference transmitter.

Prior art reference receiver

For the purpose of explaining the basic implementation method of the improved MANET algorithm, either a 2-transmitter reference configuration or a 4-receiver reference configuration is selected as the reference receiver.

3A shows a block diagram of a prior art reference receiver with two independent receive channels. The solid line represents the radio frequency (RF) path, and the dotted line represents the control path. This receiver architecture includes at least two independent receive paths, each receive path providing a separately programmable receive channel. The reference receiver 30 includes a global band preselector 31 that selects a range and transmits it to a global low noise amplifier (LNA) 32 for amplification. The global range is divided into sub-bands by programmable preselector filters 33a and 33b. Mixers 34a and 34b with variable frequencies, f ₁ and f ₂ (2-channel version shown in Fig. 3a) and f ₁ , f ₂ , f ₃ and f ₄ (4-channel version shown in Fig. 3) The Local Oscillator (LO) signal supplied to is generated by independent synthesizers 35a and 35b, respectively programmed by the control unit 36. The LO signal, sub-band range, and gain control level are dynamically determined by the digital control unit 36, depending on the receiving method used and the frequency and intensity of the desired receiving channel. The output of the mixer is a common low-intermediate frequency (IF), signal processing unit 37, usually of the FPGA type (due to the high processing speed required) that performs signal sampling (to the IF frequency) and simultaneous digital processing of all channels. ).

Multichannel receivers with up to four independent channels are already commercially available. For example, Rockwell-Collins offers a "FlexNet-Four" that includes up to four independently programmable receivers on the HF/VHF/UHF band (2 ÷ 2000 MHz). The IAI/ELTA (Elta) provides an "ARC-840D" that is independently programmable on the VHF/UHF band (30 ÷ 1220 MHz), and comes into two-receiver and four-receiver configurations. Therefore, it has been demonstrated that a receiver architecture with up to four independent receivers is feasible. More independent channels can be easily added by replicating the parallel branch.

3B shows a block diagram of an extended version (of FIG. 3A) with four independent receive channels. The solid line represents the radio frequency (RF) path, and the dotted line represents the control path. Since the complexity of the hardware increases rapidly, more than 4 channels may lack reality. Similar arrays can be known by any skilled artisan.

Improved MANET reference receiver

3C shows a block diagram of a reference receiver according to one embodiment of the present invention. The solid line indicates the RF path, the dotted line indicates the control path, and the wide arrow indicates the data bus. For example, it is possible to configure a receiver capable of simultaneously receiving the entire band with sufficient dynamic range, using the 225-400 MHz UHF band generally allocated for airborne communication. The technologies that enable these receivers are (1) analog-to-digital converters (ADCs) that perform signal sampling directly at radio frequency (RF) and practically set limits on the bandwidth and dynamic range of the system. , (2) It is a digital signal processing unit that is implemented by using a field programmable gate array (FPGA) when processing the entire RF band at a time and typically handling a high bandwidth system. This receiver architecture is currently viable for a variety of systems. Digital processing power is sufficient for ADC technology as well as for almost all applications today, which is sufficient for most systems requiring the highest possible dynamic range. An example of a modern ADC that can be used to implement a broadband reference radio receiver is National Semiconductors''ADC12D1800', a dual channel ADC with a maximum sampling frequency of 1800 MHz on each channel. These devices are specifically aimed at broadband software defined radios. Therefore, unlike prior art receivers that only receive a few channels at a time, by dividing the band into sub-bands and then reprogramming the frequencies of the channels, the reference receiver processes the entire band at once, i.e., receives all channels simultaneously. do.

Reference transmitter

4 shows a block diagram of a reference transmitter capable of operating in both broadband and frequency hopping modes according to one embodiment of the present invention. The solid line indicates the RF path, the dotted line indicates the control path, and the wide arrow indicates the data bus. This transmitter architecture is most likely chosen by those skilled in the art for broadband applications. Samples of the modulated signal right at the final frequency are mathematically generated in digital form by the signal processing unit, such as the'AD9739A' (Analog Devices) capable of operating at speeds of up to 2.5 giga-samples/second. It is converted to analog form by a high-speed digital-to-analog converter (DAC). Signal samples from the DAC are converted to analog form by a global band reconstruction filter and pre-amplified by a low-level RF amplifier. This signal is then fed to a power-controlled attenuator whose attenuation level is dynamically controlled by the control unit. The global band filter at the output of the attenuator eliminates the far-out distortion product caused by the pre-amplifier. The filter output is fed to an RF driver that amplifies it to a level sufficient to drive the final PA (power amplifier) to the maximum allowed transmit power. The output from the PA passes through a global band harmonic filter that removes the PA component which is a multiple of the transmission frequency, and then the signal reaches the transmit antenna.

MANET improves spectrum efficiency

The present invention proposes a new MANET implementation method that uses spectrum more efficiently than the prior art, and provides a higher data rate and shorter latency than the existing MANET implementation method. The improved MANET system proposed by the present invention simultaneously receives several channels (using a prior art reference receiver) over the entire frequency range (when an enhanced MANET reference receiver is employed) or a wideband frequency range in an environment of the MANET architecture. In order to do so, the functions of the reference receiver are utilized.

Practical feasibility

The improved MANET algorithm proposed by the present invention uses a half-duplex transceiver. The half-duplex transceiver is flexible and easy to implement, as it only considers protecting the receiver from burning-out during transmission. In one possible implementation, this protection can be achieved easily and inexpensively using a simple unit known as an "antenna switch" that can operate accurately regardless of operating frequency.

Use of improved MANET to improve time efficiency of conventional MANET

In a conventional MANET system, the relative physical distance between all two nodes is a result of operating requirements in the field. Typically, the distances are not known a-priori, have random lengths, and can be very different from each other. For example, in the MANET system shown in FIG. 5, the D node is close to the B node, but is far from the A node. The time delay due to electromagnetic wave propagation from node A to node D is d.

If both the B and A nodes want to transmit to the D node, the propagation time of the A to D transmission will be longer than the propagation time of the B to D transmission. According to the conventional TDMA scheme, since the D node listens for a fixed length of time slot to receive each node in the system, if the transmission of the A node arrives with a delay, some or even all of the data packets This can be lost. This occurs because the D node will switch to the frequency of the other node before all data from the A node reaches the D node. In addition, even in frequency hopping mode where the node hops through several frequencies during a single TDMA time slot, the same phenomenon because the D node will hop to a new frequency before all transmissions from A on the current frequency hop reach the destination. This happens. To overcome this problem, in prior art frequency-hopping/TDMA schemes, at the end of every time slot (whether there is only one frequency hop or more than one in the time slot), the physical layer is within the system. By pre-assigning a “protection time” equal to the maximum propagation delay that may occur, both short and delayed transmissions can arrive at the destination before the receiver is allowed to hop to the next frequency. This guard time adds an idle period to the time slot, slowing down the TDMA cycle and making the system time-efficient.

The system according to one embodiment of the present invention allows to omit the pre-allocated protection time in the physical layer, and instead allocates the protection time upon request. This embodiment can be implemented in any prior art receiver having two or more independent simultaneous receive channels as follows. If all RF channels are ordered by sequentially indexing them according to the hopping pattern, the first receiver hops on an even-indexed frequency, and of the maximum propagation delay difference that can occur between one time slot and any two nodes. Each frequency is maintained for a period of time equal to the sum. The second receiver is exactly the same except that it hops on the frequency of the odd index, and is time-lagged by one time slot compared to the first receiver. Through this arrangement, it can be easily understood from the example of FIG. 6B that both a near transmitter with a short delay and a far transmitter with a long delay are correctly received by one receiver.

However, it will be readily understood that if the duration of the maximum possible propagation delay difference is greater than the length of one time slot, two or more receivers will be required to omit the protection time using a prior art receiver. In addition, even the basic two-receiver configuration adds significant hardware and software complexity. This challenge is overcome by using an improved MANET receiver architecture that omits protection time using one single receiver and low complexity algorithms through appropriate methods, as described below.

6C shows one embodiment of the present invention implemented using an improved MANET transceiver architecture. Here, since the receivers "watching" all the channels at the same time, the receivers will always be prepared regardless of the delay length, so there is no limitation on the delay length, and unlike conventional transceiver implementations, channel indexing or There is no need for receiver time slot synchronization, substantially reducing both hardware and software complexity. In addition, the receiver need not know the frequency hopping sequence of the transmitter.

The omission of the fixed protection time significantly improves the time utilization. 6A, 6B, and 6C show a special case of the MANET of FIG. 5 in which there is only one frequency hop in each transmission and the maximum propagation length, d (corresponding to a physical distance) is equal to the duration of a single time slot. In Fig. 6A, the fixed protection time allocation consumes 50% of the cycle time. The time efficiency improvement due to omission of the protection time in FIGS. 6B and 6C is significant. In addition, the guard time can be saved in other TDMA schemes with more than one frequency hop per time slot and/or with a maximum delay shorter than the frequency hop period.

Since the enhanced MANET operates in half-duplex mode, when switching from receive to transmit, all receive paths are disconnected. Therefore, Forward Error Correction (FEC) code is introduced to compensate for possible loss of the "tail" of the last received time slot before reaching the transmission state. However, in general, an enhanced MANET system will remain in receive mode for multiple time slots before switching to transmit mode, so FEC will be needed to correct only a small percentage of the total data blocks. Therefore, the FEC rate can be made high, and the net data bit rate is not noticeably reduced.

The above examples and descriptions are provided for illustrative purposes only, and are not intended to limit the invention in any way. It will be understood by those skilled in the art that the present invention can be carried out in a wide variety of ways using one or more techniques from those described above, all of which are within the scope of the invention.

Claims (11)

As a method of reducing the protection time of a mobile ad hoc networking (MANET) system during reception,
a) At each node, with a hopping transmitter:
al) a plurality of narrowband independent receivers capable of receiving and processing at least a portion of the operating band allocated to the system at a time and including a dynamically selected channel frequency within a wide operating bandwidth, or
a.2) providing a transceiver architecture comprising a combination of non-hoping broadband receivers capable of receiving and processing the entire operating band allocated to the system at one time;
b) while maintaining the architecture of the MANET system, simultaneously receiving at least several channels randomly spread over a frequency band allocated to the system;
c) determining a transmission hopping pattern to use the minimum possible number of frequencies;
For each transport node,
d) finding a time slot in which the corresponding transceiver in each remaining active node is not transmitting and a frequency channel in which the corresponding transceiver in each remaining active node is not transmitting;
e) determining a transmission frequency of the frequency channel; And
f) if the transceiver in the transmitting node is not transmitting in the slot, receiving a transmission,
Whenever a plurality of narrow-band independent transceivers are used for reception, before switching from receiving to transmission, a transceiver transmitting to the plurality of narrow-band independent transceivers allocates a protection time to a time slot when there is a transmission request, A method of reducing the protection time of a mobile MANET system during reception, characterized in that no protection time is allocated to the time slot if there is no request. delete The method of claim 1, wherein the nodes receive and transmit using a full-duplex or half-duplex transceiver, thereby reducing the protection time of the mobile MANET system during reception. The method of claim 1, wherein the protection time is:
a) sequentially aligning all RF channels by sequentially indexing the RF channels according to the hopping pattern;
b) let the receiver hop on an even-indexed frequency, and keep it on each frequency for a time period equal to the sum of the maximum propagation delay differences that can occur between any two nodes and one time slot; And
c) by causing the other receiver to hop on the frequency of the odd index, and to be maintained on each frequency for a period of time equal to the sum of the maximum propagation delay differences that can occur between one time slot and any two nodes,
A method of reducing the protection time of a mobile MANET system during reception, characterized in that it is allocated on request. The method of claim 1, wherein the protection time is not allocated to the time slot. The protection time allocated to the time slot according to claim 1, wherein a conventional receiver having two or more independent simultaneous reception channels is used:
a) aligning all RF channels by sequentially indexing according to the hopping pattern;
b) cause the first receiver to hop on an even-indexed frequency, and keep on each frequency for a time period equal to the sum of the maximum propagation delay differences that can occur between any two nodes and one time slot; And
c) The second receiver, which is staggered in time by one time slot compared to the first receiver, causes the second receiver to hop on the frequency of the odd index, and may occur between one time slot and any two nodes. By keeping on each frequency for a period of time equal to the sum of the maximum propagation delay differences,
A method of reducing the protection time of a mobile MANET system during reception characterized by being reduced. The method of claim 4 or 6, wherein the duration of the maximum propagation delay difference is greater than the length of one time slot, the protection time is omitted by using two or more receivers, characterized in that the mobile during reception How to reduce the protection time of a MANET system. The method of claim 1, wherein when a single broadband receiver is used, the guard time is omitted without channel indexing or receiver time slot synchronization. The method of claim 1, wherein the guard time is reduced to have one or more frequency hops per time slot. 7. The method of claim 4 or 6, wherein the protection time is reduced to have a maximum delay shorter than the duration of hopping on the frequency. A mobile ad hoc networking (MANET) system with reduced protection time during reception,
a. A transceiver architecture provided for each node, with a hopping transmitter:
al) a plurality of narrowband independent receivers capable of receiving and processing at least a portion of the operating band allocated to the system at a time and including a dynamically selected channel frequency within a wide operating bandwidth, or
a.2) comprising the transceiver architecture with a combination of non-hoping broadband receivers capable of receiving and processing the entire operating band allocated to the system at one time,
The MANET system is:
b. While maintaining the architecture of the MANET system, simultaneously receiving at least several channels randomly spread over a frequency band allocated to the MANET system;
c. Determine a transmission hopping pattern to use the minimum possible number of frequencies;
d. For each transmitting node, find a time slot in which the corresponding transceiver in each remaining active node is not transmitting and a frequency channel in which the corresponding transceiver in each remaining active node is not transmitting;
e. For each transmission node, determine a transmission frequency of the frequency channel; And
f. For each transmitting node, if the other node did not select the same time slot and the transceiver in the transmitting node is not transmitting within the slot, it receives a transmission, and at the same time relay nodes use different channels. Allow simultaneous transmission;
g. Whenever a plurality of narrow-band independent transceivers are used for reception, a transceiver transmitting the plurality of narrow-band independent transceivers to the plurality of narrow-band independent transceivers before switching from receiving to transmitting allocates a guard time to a time slot when there is a transmission request, If there is no mobile MANET system having a reduced protection time during reception, characterized in that the time slot is not assigned a protection time.

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