FR3089725A1 - Transmission method in a heterogeneous V2I system, server and corresponding system - Google Patents

Abstract

Transmission method in a heterogeneous V2I system, server and corresponding system The invention relates to a data transmission method, the data coming from messages intended respectively for terminals, via at least a first millimeter band access network comprising relays. distributed in space according to a determined density λ or via a second access network with a frequency band below 6 GHz comprising so-called macro base stations, such that a choice of the access network is made before each transmission on the based on a comparison between estimated bit rates with each of the access networks, the message intended for the terminal comprising B segments coded in the form of binary signals. According to the invention, the method comprises: estimating a state of a transmission channel between the relays and the terminal at a current transmission interval, transmission in a data packet selected from the current binary signals and the binary signals already transmitted knowing the estimated overall state of the transmission channel. Figure for the abstract: Figure 5

Description

Description

Title of the invention: Transmission method in a heterogeneous V2I system, server and corresponding system Field of the invention

The field of the invention is that of data transmission in a telecommunications network. More particularly, the data is transmitted to moving terminals either via relays of a first access network, or via a macro site of a second access network, the first access network and the second network. access forms the heterogeneous access network.

The invention relates more particularly to techniques for the simultaneous transmission of data from one or more source nodes to two or more terminals in motion via a heterogeneous access network.

We distinguish in the context of the invention an access network with millimeter waves which range between 30 and 300 GHz in which the base stations are called relays and an access network with a band less than 6 GHz in which the base stations are called macro SB. The congestion of the channel in the frequency band below 6 GHz makes the millimeter-wave access network attractive, given the available bandwidths and therefore given its transmission potential.

The transmission between the access network and the mobile terminals is done by a propagation channel whose characteristics depend on the frequency band for the transmission. In particular, millimeter waves are much more sensitive to blocking phenomena by an obstacle in the propagation channel than waves of frequencies below 6 GHz.

Thus, in the context of the invention, the propagation channel considered for the millimeter band access network is said to be erasing (this channel is characterized by a probability of erasing the data), while in the case of an access network with macro SB we distinguish an attenuation effect and a multi-path effect of the propagation channel modeled in free space by an equation taken from the so-called Friis law. According to a simple modeling considered for the invention, the erasure propagation channel is such that beyond a given distance Rb of a relay, the transmitted signal no longer has enough energy to be received correctly. In other words, a terminal remote from any relay greater than Λ b receives no signal from these relays. Only a terminal located at a distance less than R b from a relay receives data transmitted by this relay.

The deployment of vehicles with ever more autonomy requires data exchanges not only between vehicles, so-called V2V transmissions but also between vehicles and a server via relays, so-called V2I transmissions. For example, data on the state of the traffic lights, on the state of the roads (works, blocked roads), on speed limits will be disseminated to vehicles. Access to this data will make it possible to deploy supervised driving services with control, for example, of speed, accelerations, braking, distances between vehicles with safety objectives, controlling energy expenditure.

The invention takes place in the more specific context of V2I transmissions with data dissemination to mobile terminals.

[0008] Conventionally, the mobile terminal goes back to its geographical location obtained for example by means of positioning functionality via satellites (GPS, Galileo, etc.). Of course, other mechanisms exist for the access network to obtain the geographic location of the terminals, let us quote for example triangulation mechanisms.

[0009] Conventionally, when a mobile terminal receives a data packet, it sends an acknowledgment message to the relay: Ack for an acknowledgment of the packet and Nack otherwise. Thus, downlink data transmissions are acknowledged by an Ack or Nack message. Such an acknowledgment allows the data sender to know the state of the channel (Ack for a received packet or Nack for an erased packet) which existed during the transmission of this data.

Given the mobility of the terminal and the characteristics of the millimeter channel, the state of the channel can totally change between the previous transmission interval to which the rise in the state of the channel corresponds and the current transmission interval.

Prior art

Certain known methods use beam alignment techniques to increase the throughput by focusing beams on the terminals to be served. Other methods implement a specific timing between V2I transmissions and transmissions between V2V vehicles to maximize the overall throughput. Statement of the invention

The invention provides a transmission method which exploits certain characteristics of a propagation channel to make a heterogeneous V2I system more efficient.

More particularly, the invention relates to a method of transmitting data packets, the data coming from K messages intended respectively for K terminals, via at least one first millimeter band access network comprising distributed relays in space according to a determined density λ or via a second access network with a frequency band below 6 GHz comprising so-called macro base stations, such that a choice of the access network is made before each transmission on the base a comparison between estimated bit rates with each of the access networks, the message Mk intended for the terminal k comprising B segments ^m k, i>, mk, b coded in the form of binary signals

VfcX. ' - ^K = X ”& = [X -. S + K - 1] ' ^PrOœde includes for the different terminals k;

- estimation of a state ç of a transmission channel between the relays and the k, t _b terminal k at a current transmission interval t _b knowing the density λ of the relays, a location of the terminal k at an instant. φ. prior to t & - l _s the current transmission interval t _b and an average speed ^v k of movement of the terminal, the channel being considered of the erasure type beyond a given distance R b around each relay and comprising : at the current transmission interval, transmission of data selected from the current binary signals V _kh and the binary signals already transmitted _ ₁ knowing the estimated overall state λ _r _ [4 ç] of the transmission channel between the relays and the terminals at this current interval and knowing the overall actual state c 1 of the transmission channel between the È — 1 'it relays and the terminals at a transmission interval prior to the current transmission interval t

The invention consists in adapting the flow of data to be transmitted according to the estimated state of the channel of each terminal for which a message is intended, the estimation being carried out for the current transmission interval, and to retransmit to this same data interval based on the actual state of the existing channel during the previous transmission interval.

Based on knowledge of the density of base stations, the average speed of the terminal and its location at an instant before the current interval and considering an erasure channel when the selected access network is a millimeter network, it is estimated a binary probability of good reception of the data.

An erasure type channel is such that the probability that a terminal receives the transmitted data is one if the terminal is at a distance from a relay less than the given distance Rb and zero if not. The distance K-b given can be determined for example during measurement campaigns or evaluated using a propagation model knowing the transmitted frequency, the transmission power and the antenna gain. The distance Rb is an approximation of the range of a relay.

When the probability is one the channel state is one, the channel state is zero if not. Thus, the state of the channel is estimated for each terminal.

The invention thus makes it possible to transmit a current binary signal to a terminal only if the estimated state of its channel is one and otherwise to keep it for transmitting it later depending on the actual state of the channel.

Although transmissions in a millimeter band are very sensitive to obstacles, the method makes it possible to limit erroneous reception by a moving terminal by avoiding transmitting to this terminal when it has a very low probability of correctly receiving the data. . The invention thus makes it possible to increase the overall speed of transmissions to the terminals.

The proposed method goes against the methods known in the field which work to improve the timing between V2I transmissions and V2V transmissions or which implement beam focusing to avoid obstacles present in the channel in that '' it relies on one or more macro BS offering a low speed but good coverage and a network of relays operating the millimeter band offering a high sporadic speed and low coverage. In addition, the proposed method is based on an estimate of the future state of the channel and on a knowledge of the past state of the channel to transmit pending data (possibly already transmitted but not correctly received).

According to a particular embodiment, the data to be transmitted are in a.-2 parts including the

F K respective lengths are in data packet reports and the packet includes at most 2 4 of the packet length with

And the method is such that the coding efficiency of a binary signal to be transmitted at the current transmission interval is adapted to be transmitted in one of the parts of the packet, the values of the coefficients being determined as a function of the estimated and real states of the transmission channel to obtain an optimal sum flow.

According to this embodiment, the selection of the data comprises an adaptation of the performance of the binary signals which must be transmitted so as to obtain a maximized sum bit rate.

According to a particular embodiment, the determination of the maximum sum flow is obtained by an exhaustive search during which the sum flow is calculated for different combinations of the values of the coefficients.

According to a particular embodiment, the packet can include K first parts reserved for current binary signals.

According to a particular embodiment, the packet may include a last part reserved for binary signals already transmitted at a previous transmission interval, _e j - - 2 + Cj] ·

According to a particular embodiment, the packet can include parts reserved for combinations of current binary signals.

According to a particular embodiment, a combination of binary signals is a bit-to-bit binary addition of two current binary signals.

According to a particular embodiment, the state of the transmission channel between the relays and a terminal is determined by taking into account a return from the terminal upon receipt of transmitted data.

The invention further relates to a server, the server being able to be hosted in an access point of a first millimeter band access network comprising access points distributed in space according to a density λ determined or from a second access network with a frequency band below 6 GHz comprising so-called macro access points

Such a server can of course include the various characteristics relating to the transmission method according to the invention, which can be combined or taken in isolation. Thus, the characteristics and advantages of this server are the same as those of the transmission method and are therefore not described in more detail.

The server can be a server located in a core network. It can be a component of a network currently called "cloud" in English terminology.

The server can just as easily be hosted in a relay, in a base station or in a central element of an access network such as a scheduler ("scheduler" according to English terminology).

The invention further relates to a telecommunications system comprising at least a first millimeter band access network comprising access points distributed in space according to a determined density λ and a second access network of frequency bands lower than 6 GHz comprising so-called macro access points for transmitting data packets, such that a choice of the access network is made before each transmission on the basis of a comparison between estimated bit rates with each of the access networks, the data coming from K messages intended respectively for K terminals, the message M intended for the terminal / <comprising B segments ^m k, 1 '· ^m k, B coded in the form of binary signals. ..,> 2, k = 1, = [1, + Æ - 1] 'including:

- a computer to estimate a state ç of a transmission channel between k, t _b the relays and a terminal k among the K terminals at a current transmission interval tb knowing the density λ of the relays, a location of the terminal k at a instant τ _ τ prior to the transmission interval ^l s current t and an average speed ^v k of displacement of the terminal, the channel being considered of erasure type beyond a given distance R b around each relay,

- a computer for selecting data to be transmitted in a packet, among the current binary signals V _k and the binary signals already transmitted V _{kh 1} knowing the overall state

AT . c c estimated transmission channel between

1, tb k, ti)

[0034]

[0035]

[0036]

[0037]

Relay and terminals at this current interval and knowing the overall state S ’,; = [S, ..., S, _] real of the transmission channel between the relays and the terminals at a transmission interval earlier than the current transmission interval f / ->.

A transmission method according to the invention can be implemented in the form of a digital or analog integrated circuit, or in an electronic component of microprocessor type.

Thus, the transmission method according to the invention can be implemented in various ways, in particular in wired form or in software form.

In particular, the invention may be declined in one or more computer programs comprising instructions for the implementation of a transmission method as described above, when the program or programs are executed by a processor of a server , one or more access points. Such programs can be stored on an information medium.

List of Figures

Other characteristics and advantages of the invention will appear more clearly on reading the following description of particular embodiments, given by way of simple illustrative and nonlimiting examples, and of the appended drawings, among which:

[fig.l] FIG. 1 schematically represents a V2I system according to a known architecture,

[Fig.2] Figure 2 is a schematic representation of the probability function associated with the erasure channel model considered in the context of the invention,

[Fig.3] Figure 3 is a schematic representation illustrating the surface corresponding to the estimate of probability of a connection of the mobile terminal with a relay and the actual surface when the mobile terminal moves with a speed ^v k and that T _s is the time difference between the acquisition of the location of the mobile terminal and the current transmission interval for which the channel is estimated,

[Fig.4] Figure 4 partially shows the representation of Figure 3 with further aspects of geometry,

[Fig.5] FIG. 5 schematically represents a V2I system according to a heterogeneous architecture,

[Fig.6]

[Fig.7] Figures 6 and 7 show performance curves from simulation,

[Fig.8] Figure 8 is a diagram of an access point hosting a server according to the invention according to one embodiment.

Description of embodiments of the invention

A V2I system illustrated by the diagram in FIG. 1 comprises at least one server S connected by wire to relays R of an access network operating in a millimeter band. Data transmissions from a server S to mobile terminals Cl, C2, C3, ... .CK in motion are relayed by relays R to which the mobile terminals are connected by radio. Such a V2I system is said to be homogeneous because it comprises a single access network with relays of the same type (operating in the same frequency band).

Each mobile terminal k moves with an average speed ^v k.

Given the frequency band (millimeter) for radio transmission, the propagation in the channel suffers from blockage more particularly when an obstacle is located between a relay and the mobile terminal. The state of the channel changes over time, given that the terminals are in motion, even if an obstacle can be fixed. After each reception of a data packet relayed by a relay, a mobile terminal goes back to the server via the relay the state of the channel. This feedback can be done using an ARQ (Automatic Repeat Request) mechanism with an ACK / NACK agreement.

According to the invention, the wave propagation model is considered to be of the "Line of Sight ball blockage chanel model (Ref 1) type, called line of sight obstruction channel. According to this model, the probability for a link to be in the crosshairs of a relay is one if the distance between the relay and the mobile terminal is less than a determined distance R g and zero beyond.

According to this model, the probability is a unit step function illustrated in Figure 2

P _LoS (d) = l (d <R _B ) (D

With 1 (.) The unit step function and R b the maximum distance for a link in direct view.

Considering that the LoS condition is necessary and sufficient to acknowledge receipt of a packet sent by the relay, a mobile terminal can correctly receive a signal if it is in a circle of radius R b centered on the relay considered. Otherwise the package will be declared deleted. It follows

PLos (d) = P _c (d) where P (d) represents the probability ^s k, t ^{= 1 s} k, t ^{= 1} of a packet acknowledgment. According to this model, the system's propagation channel is of the broadcast erasure type (EBC: Erasure Broadcast Channel). The following notations are used:

- channel state variable at time t for user k: S _{ • S k _t = 0 if there is erasure (state corresponding to a NAck) • S _kt = 1, otherwise

- overall state of the channel at time t for all K mobile terminals:

S _t : = [$! _t , ..., S _{K r} ]

The overall state of the channel is available to the server S with a delay of a transmission interval relative to the current transmission interval, given that the ascent from the mobile terminal to the server occurs after the reception and decoding of the data. . Thus, at the current transmission interval the server knows the state of the channel S _z f / 2-1

According to the invention, the server estimates the state of the channel at the current time t p of transmission:

[0058]

[0059]

(2)

The corresponding Markov chain is therefore:

*% -i

y. <> ^c û + l (3)

To make this estimate, the server uses the location of the vehicles. This location is noted g (t). The relays are considered distributed in space according to a Poisson law (PPP Poisson Point Process) of density λ. Thus, in a surface area A the average number of relays is λ A. Consequently, the probability that there is ⁿ relay in an area A is given by the Poisson distribution:

[0062]

- ·. (4)

F (, ¥ = „) ₌ n!

The probability that a mobile terminal k is not connected at time 1 is given by:

[0064]

P (5 ^ _t = 0) = P (M = 0) = P (4r = 0): = e “^ ⁽⁵⁾

With _ 77-J ^ the surface of the circle of radius R b

3 shows a mobile terminal in motion at a certain speed ^v k.

Given the speed of movement of the mobile terminal and given that the current state of the channel is estimated by the server from only the location information g (t) reported by the mobile terminal k then this state estimated may be different from actual state. If the speed of the mobile terminal is low then the estimate is relatively precise on the other hand if the speed is high then the estimate is relatively imprecise.

Let T _{s be} the time offset between the instant of acquisition of the location information of the mobile terminal and the current transmission interval tb, or ^v fc the speed of the mobile terminal k, then the area taken into account for the estimation of the channel, A _f _ _T is represented in the diagram of FIG. 3 by a dotted circle of radius R b around the mobile terminal whose location g (t _b - T ₅ ) is that returned to the server and acquired at time tb ~ T _s .

But the actual state of the channel for the mobile terminal k is that which corresponds to the surface inserted in the dark edge circle and which corresponds to the location g (t) of the mobile terminal at time fb such that illustrated by figure 3. This surface inserted in the dark edge circle is distinguished from the surface inserted in the dotted circle by the surface A _k (hatched surface). The estimated state A of the channel for k, t _b mobile terminal k at the current transmission time t _b corresponds to the actual state

S, of the channel:

k,

If there is no relay in the surface circle A centered on g - T _s ) then there is also no relay in the truncated circle of surface A ^ (hatched surface) centered on ^100711: F (5i :, _th = 0 |% ₆ = 0) ·

If there is a relay in the truncated circle of surface A ^ (hatched surface) centered on g (tb-T _s ) then there is also a relay in the truncated circle of surface A (hatched surface) centered on ¹⁰⁰⁷³¹ g (t ₆ ): P (s _fcri> = 1 | S _W6 = 1) '

If there is no relay in the truncated circle of surface A ^ (hatched surface) centered on g (f - T _s ) then there is a relay in the common part of the circles of surface A centered on g (f,) and _{; = =} 0.

The following relationships established in connection with Figure 4 which shows the geometric representation of Figure 3 can determine this hatched area (truncated circle) A _k .

.

Surface ^^ = ùJr _b ² - h ²

Swface ^^ U = ~ kR _s ² = = R _s ² cos- ¹ N-}

Surface ^ = Surface ^ o ~ ~ Surface _ÂOB . , / h \! ,,, LîATA Vi / E i:

= RZ "MT ¹ , - R? = R _b - eus- ¹ 5 JJ ⁷ \ Κ _δ / 4 \

Hence the expression of the surface A _k (hatched surface):

[0077]

"..Tt = A - 2 * Sitr fàce ^ g ¹⁶ '^ - A +

ZN (^ T _s ) ² --2Re ² COs-M '^ ^S )

For each mobile terminal k, the distance between its actual location and the location which corresponds to the feedback of location information to the server is: V _k T _s . The hatched area of Figures 3 and 4 is therefore given by the relation:

¹⁰⁰⁷⁹¹ A _k - A + ^ Rd- ^ _k T _s Ÿ-2R _B ² arcos ()

This surface A _k increases with speed ^v k from a value of zero to the value A and remains constant at this value A when

V _k T _s > 2R _B.

Given the distribution of relays in space and the line of sight obstruction channel model, then the probability that the real state is zero while the estimated state is zero is given by:

[0083]

[0084]

And the probability that the real state is zero while the estimated state is one is given by:

P (S _fcI = 0 | S _fc e (7).

j _t;

[0086]

[0087]

Indeed, - θl'Sfc.e - θ) ⁼ of BS in the surface A _k ) = e pis - Ois = i) = ~ ~ -0 _ ⁼ θ) ^{x =} M ^g fe, Î - θ) ^{1 feiÎ} ~ ^J ~ 1) ~ 1 - P (4 _t = 0)

XP (S _{fe> t} = LS _fct = 0) _ x = 0] S _{fe; £} = 0) J _ _e - ^ (l 1 - q _ _g --M. | _ _E -7A

The mobile terminals being located in space independently, then the probability that the actual overall state of the channel is equal to ^Λ and that the estimated overall state of the channel at the instant ΐ μ is equal to s can write:

¹⁰⁰⁸⁹¹ P (S = Ss = s) = Π »ρ (4 = 4) p (x = = 4) Vs.se (O, 1) ^K (8)

By way of illustration only and for a clear description, the case of two mobile terminals is considered below, K = 2.

In general, the information messages are divided into blocks (here the number of B). Each block receives redundancy bits from the Cyclic Redundancy Check (noted CRC). At each transmission instant, the server transmits a data block which includes a CRC to provide an ARQ mechanism (a reception error is detected on the basis of the CRC). Kl blocks for the transmission of common messages are added. To transmit two messages Μγ, M ₂ respectively to the two mobile terminals, the server therefore has

B + K - 1 = B + 1 transmission intervals. At each transmission interval, the server transmits data with at least one CRC to trigger an ARQ mechanism if a reception error is detected on the basis of the CRC.

Each message Μχ, M- ₂ is divided into B segments ^m 1. b, ^m 2, b with b G [1, B] to be coded according to a coding called source coding to generate binary signals Vf. _h and then to be transmitted during the first B transmission intervals. Once the transmission at the transmission interval tb - 1 is finished, the state of the channel B _{k {} is returned by each mobile terminal k.

At the start of the current transmission interval tb, the server uses the latest location information g (t ~ T _s ) of each mobile terminal to estimate the state of the channel $ for the transmission of the current data packet to this interval of tb current transmission. Knowing the 5 '* reassembled state and the estimated state A of the channel, tfe-1 a, the server queue can decide which binary signals to transmit or retransmit and the respective proportion of time that it allocates to them to maximize the sum throughput. of the two flow rates of each vehicle.

Each transmitted data packet can comprise two parts of data of fixed overall length but the respective lengths of which can be adapted as a function of the two real S and estimated states. The first part is said to be private, th that is to say contains data not yet transmitted, the second part is said to be common, that is to say contains data already transmitted (and not received correctly) but which can benefit to several users to facilitate the decoding of the binary signals already transmitted. The private part includes as many parts as users plus as many parts as combinations of binary signals. In the case K = 2, there is only one combination, three parts for the private part. The respective lengths of the parts are determined to achieve the best sum transmission rate. These respective lengths are determined by the values of the coefficients (X χ, (X ₂ , G 3, G 4 = 1 - G χ - G ₂ ~ G 3, each coefficient giving the length of the corresponding part of the packet relative to the total length of the package.

The first transmitted data packet includes the only private part of data to transmit the current binary signals ₁₅ V ₂ ] as well as the combination of the binary signals Vj -] χ · The combination can be for example the binary sum after coding of current segments. The coefficient CX 4 = 0 because there was no transmission before this current transmission and therefore no retransmission is to be considered.

The B - 1 following data packets include the two parts, private and common, of data to be transmitted. The first private data part is reserved for transmitting the current binary signals V ₂ b G [2, B] and possibly a combination of these current binary signals denoted Vj (X) V ₂ μ This first part therefore comprises three sub-parts, of which the respective lengths are determined by the values of G 1, G ₂ and G 3. The second common data part is reserved for retransmitting one of the binary signals already transmitted _ _χι V ₂ h -1 "G [2, B], says common signal V _{0; b} _ _r The length of this second part of the data is determined by the value of α ₄ = 1- α ₁ -α ₂ ^_σ 3 ·

The B + 1 data packet includes only the common data part for retransmitting one of the binary signals already transmitted V _LB , V _{2 B} said common signal, (X 4 = 1 since there is no more signal current binary to transmit.

Based on the knowledge of the state of the channel S _f raised, the server generates the common signal V _{Q h} _ j to be transmitted at the next transmission interval, t b. The common signal Vq _b _ _L can be generated for example in accordance with table 1 in Annex A.

Given the relationships (5) - (8), it is possible to define the probability vectors:

[OiOO] _p ^ ₌ [ _p ( _{s = S)} S = s) {00,01,10,11}]

[oioi] p ₅ is the joint probability vector that the real state is S = s and that the state

[0102]

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

Estimated has one value among all possible values. For example is the joint probability vector that the real state is 5 '= 01;

P _O1 = [p (s = 01, S = 00), p (s = 01, S = 01), p (s = 01, S = 10), p (S = 01, S = 11)] ™ ₌ | ¹ p is the marginal probability.

We also define P j the joint probability vector that the real state S 'is not ^s and that the estimated state has a value among all possible values. For example PO! is the joint probability vector that the real state is not 5 = 01:

Ρδϊ = 00), p (S + 01, S = 01 + 01, S - 10), p (Sj # 01, S = 11)]

The rates R 1, R 2 which can be achieved by the two mobile terminals satisfy the following constraints:

Ρχ <(iq 4- a ₃ ) ^r p _w

R ₂ <(a ₂ 4 (a ₂ 4- α ₃ ) ^Γ ρ10Λ1 4- (at ri- a3) ⁷ pw <1 - ρ ₀₁₀₀ (¾ + + ("2 +" sFPw - ¹ ("i 4- a ₂ 4- α ₃ ) <1

2, ® 3 are the three vectors which represent the allocated time ratio where i, to the different data transmitted for different estimated states of the channel. "1 is a vector whose first element indicates the time ratio allocated to the mobile terminal ρ ₌ ] when S '= QQ, whose second element indicates the time ratio allocated to the mobile terminal p _ j when 5 = 01' ^ ^{οη1 'c} third item specifies the time ratio allocated to the mobile terminal j ^ z _ 2 when S' = 10 ^{and c} ^ ^have the fourth element indicates the time ratio allocated to the mobile terminal £ _ j where S = 11 · L ^a composition of the vector S 2 is similar to that of the vector di and that of the vector Œ 3 follows from the compositions of Œ 1 and 2. To optimize the flow rate ie to reach the best flow rate it is necessary to optimize these three vectors O b Cf 2, ® 3L optimization to result from exhaustive research. According to this procedure, first values verifying the constraints (9) are assigned to the vectors ^α . These values will lead to a pair of flow rates (Rp R 2) to each vehicle. The sum flow of this pair is determined. New values are assigned to the vectors ^a which will lead to a new pair of flow rates (R 1, R 2) to each vehicle, and the sum flow rate is again determined. The pair of flow rates which gives the largest sum is retained and determines the values retained of the vectors ^a . These steps are repeated a specified number of times. In the end, the procedure makes it possible to obtain the values of the vectors ^a leading to the highest sum flow.

Such an exhaustive search can be carried out beforehand and saved in a table. The method according to the invention then interrogates the table on the basis of knowledge of the probability vectors P ₅ and or on the basis of knowledge of the density of the relays, the average speed of the mobile terminals and the time difference décalage _s between the acquisition of location and transmission interval.

The data packet transmitted at the transmission interval t fa, b G [1, B + 1 J, comprises parts of data with times allocated to the parts and therefore to the segments to be transmitted determined according to the values of the three vectors O b ® 2> ® 3 [0112] After the transmission of the messages Μ j, M2, the receivers (mobile terminals) each decode all the binary signals received. The receiver k first decodes the last binary signal received V _{o B} contained in the block B + 1 to determine one of the retransmitted binary signals, V _{k B} or to determine the combination of binary signals (X) V _{2 B.} The binary signal V _B can help the receiver k to decode Vq _b _ ₁ by exploiting the received packet transmitted at the transmission interval ΐβ · This reverse decoding process (backward according to English terminology) is continued until the first packet received.

In the case where K = 3, there are B + K - 1 = B + 2 transmission intervals. The first data packet transmitted comprises only a private part comprising three parts for the binary signals V _{χ χ} , V ₂ p V ₃ and three parts for the combinations V] j (x) W, j, p V2 j V 3 j of respective lengths given by 2 ^K - 2 + C ² - = 8- 2 + 3 = 9 coefficients

Cï 1, G 2, G 3, G 4, G 5, G q, G y, G q, G g. The B - 1 following packets of transmitted data include the private part and the common part whose length is given by (I ₉ = 1-Ο ₁ -ΰ ₂ ^ίϊ 3θ4 ^ίϊ 5 ^ 6 ^ 7®8 · [0114] Both last data packets transmitted respectively to fg + 1 and fg ₊ 2 include only the common part whose length is given by G 9 = 1.

The common signal V _{o B} transmitted in the common part at the transmission interval t fa, G [2, B + 2] can be generated for example in accordance with table 2 in Annex A.

More generally for K> 2, the server has F "+ K - 1 transmission intervals. At each transmission interval, the server transmits a data packet which includes at least one CRC to trigger an ARQ mechanism if a reception error is detected based on the CRC. The K messages M4, M ₂ , ..., M _K to be transmitted to the K mobile terminals are each divided into B segments ^m l h ' ^m 2b <' m _{K b} with b G [1, B] which may not be of same length, to be coded into binary signals Vj _b , V ₂ b, ···, b P ^u i ^s transmitted during the first B transmission intervals. Each segment is coded with a determined yield.

[0117]

[0118]

[0119]

[0120]

[0121]

[0122]

Once the transmission at the transmission interval t £> - 1 is complete, the state of the channel S _th is returned by each mobile terminal k.

At the start of the current transmission interval tb, the server uses the latest location information (t ^ - T _s ) of each mobile terminal to estimate the state of channel A for the transmission of the current data packet at this interval of ^ύ t _b current transmission. Knowing the reassembled state S, and the estimated state A of the channel, tb -1 tb the server can decide which binary signals to transmit or retransmit and the respective time that it allocates to them to maximize the bit rate sum of the K bit rates of respectively K vehicles.

Each transmitted data packet can comprise two data parts of fixed overall length but whose respective lengths can be adapted as a function of the two states S and. The first part is said to be private, that is to say contains data not yet transmitted, the second part is said to be common, that is to say contains data already transmitted but which can benefit several users to decode coded segments already transmitted. The private part includes as many parts as users plus as many parts as combinations of binary signals.

The respective lengths of the parts are determined to achieve the best sum transmission rate. These respective lengths are determined by the values of the coefficients

r.K rj 2.

- 2 + CK - 1 a ₂ , .... a ₂ Ki _{+ c} 2 _ _r a ₂ Ki _{+ c} 2 with α, κ_ _{2 + c} 2 = 1-Σ, _{= 1} a,, each coefficient giving the length of the corresponding part of the package in relation to the total length of the package.

The first transmitted data packet includes the only private part of data to transmit the current binary signals V _{T x} , V ₂ ρ ·· ·> 1 ^a ^ ^ns ^ 9 ^ue ' ^cs combinations of the binary signals (§) V ₂ p Vj χ ® ^ 3 p ···, _K _ ij ® V _Ki 1 ·

The following B - 1 data packets comprise the two parts, private and common, of data to be transmitted. The first private part of data is reserved

[0123]

[0124]

[0125]

[0126]

To transmit the current binary signals ^ 2 ^ 22, ..., V _{K 2} > - · ·> K 'V ₂ K' ··· 'R' as well as the combinations of the binary signals Vj ₂ 0 V ₂ 2 'V _{1) 2} 0 ^ 3.2' ··· ' ^F K-1.2 0 2 ”·” 0 ^F 2, X' ^ 1, X 0 ^ 3, K '”·'

- 1 K 0 KK 'C ^cttc first part therefore includes several sub-parts whose respective lengths are determined by the values of d 1, (X 2, · · -, ® 2 ^Â - 2 + - 1 · The second common part of data is reserved to retransmit one of the binary signals already transmitted _b _y V _2Z , _p ..., V _Kh _ ₁ b E [2, BJ, called common signal V _{Q b} _ j. The length of this second part of data is determined by the value of (X., K _ „., 2 = 1 - (X χ - (X ₂ ^_ ~ _-y. r ² - ii 2 + L _k L. i. + L _k 1

The data packets £ + 1, B + 2 ,,. ,, B + K - 1 include only the common part of data for retransmitting one of the binary signals already transmitted, said common signal, and Ct _ ₂ + ⁼ P ^u i ^s Q ^u ü ^{n 'are} more current binary signal to be transmitted. Based on the knowledge of the state of the channel S ' _f % -1 raised, the server generates the common signal V _ob _ ₄ to be transmitted at the next transmission interval, f / _? .

After the transmission of messages Μχ, ..., Mr, the receivers (vehicles) each decode all the signals received. The receiver k first decodes the last received data packet V _{o B +} _ χ to determine one of the retransmitted binary signals or to determine the combination of retransmitted binary signals. The determined binary signal can help the receiver k to decode the common signal Υθ _{β + k} _ ₂ by exploiting the received packet transmitted at the transmission interval tg _{+ k} _ χ. This backward decoding process (backward according to English terminology) is continued until the first packet received.

The rates R χ, R ₂ >> R κ which can be reached by the K mobile terminals satisfy the following constraints:

/ „ _T x _t With

F [if] the following constraint:

max

R, .7

[0128]

[0129]

VU CJ, s r- S _c (tl _f g)

[/ ¾ & [O, 1] if 3 = M, | ùj = 131 - i ^{1 sinûn}

Where ^: = [v ^{îe S} J ^e & l] ² ® / eQwith Σ, ερ " _ç = 1 <> ù îï _:. a ₂ , .... " ₂ k_ ₂ . _{; <} l are the vectors which represent the ratio of time allocated to the different data transmitted for different estimated states of the channel. To optimize the flow, ie to reach the best flow, these vectors β i, CI 2, ···, 2 ^K -2 + C ^ must be optimized. Optimization to result from exhaustive research conducted in a similar manner to the case described for K - 2.

According to the invention, the V2I system is said to be heterogeneous because it comprises at least two access networks with relays of different type (operating in different frequency bands) as illustrated in FIG. 5. The first network d Access operates in a millimeter frequency band for radio transmission, it corresponds to the homogeneous network previously described. The second network includes so-called macro base stations BS which operate at frequencies below 6 GHz known as the 6 GHz network. The mobile terminals can be connected either via a relay R or via a base station BS. According to this mode, the invention also determines the access network to which the mobile terminal must connect to optimize the sum speed.

Each of the K mobile terminals Cl, C2, C3, ..., CK being able to connect either to the millimeter wave network or to the 6GHz network, there are 2 ^ different possible combinations for the connections. The server calculates the maximum throughput that can be achieved by each of the combinations. When the connection is via a relay, the speed is calculated using the relationships (6) - (8). When the connection is via a base station, the speed is calculated for a MU-MISO scheme. The server then compares the maximum sum bit rates that can be reached by each of the 2 ^K combinations of different possible connections and selects the one which provides the maximum sum bit rate. The server informs the relays and stations of the best connections for each mobile terminal.

The taking into account of the macro SB leads to making a hypothesis of transmission scheme. Thus for each mobile terminal, the delivery of the signal by a relay or by the base station leads to two transmission hypotheses. By making the assumption of a communication with 2 mobile terminals, the optimization is made on the basis of these assumptions and leads to a pair of bit rates (R χ, R 2) to each mobile terminal. Thus the following sum debit couples can be estimated:

• For the transmission scheme where the macro SB serves terminal 1 and the relays serve the terminal 2: (R χ, 0, 0, R ₂ ) • For the transmission scheme where the macro SB serves terminal 2 and the relays serve terminal 1: (O, R ₂ ; R χ, 0) • For the transmission diagram where the SB macro serves terminals 1 and 2:

For the transmission diagram where the relays serve terminals 1 and 2:

(0.0; R p R 2)

[0134]

[0135]

[0136]

The bit rate reached with the use of the macro base station SB can for example be based on an estimate of the theoretical capacity C of the channel weighted by the number of terminals considered. In the case of a SISO channel this theoretical capacity can be expressed in the form x- · _ ta / (i 1 S \ and in the case ΜΙΜΟ in the. In these expressions W reform _{c = m] jn (n} present the base station bandwidth, S the signal to noise ratio, ⁿ 1 " ⁿ the number of antennas respectively on transmission and reception. Once the transmission diagram has been determined, this diagram is maintained for the transmission of the B blocks. This implies that the B blocks are either supported until reception of the B blocks by the SB macro or by the relays.

FIG. 6 illustrates the region of the speed that can be reached in the case of a homogeneous network with two mobile terminals. Relay density is = 4 / k 771 ² 'delay T _s = 10s, length R = 0.2km The two mobile terminals move at the same speed v 1 = v ₂ = 60k m / h OR V x = V ₂ > 144k m / h. For each of these two speeds, the sum flow curve is greater than the sum flow curve obtained in the case of channel sharing according to a TDMA scheme. The limit of the total flow that can be obtained is given for a zero speed:

Vi = v ₂ = 0km / h.

Indeed, when the speed is zero, the information of the current state is perfectly known whereas if 2R r. . the information of the current state is v> = 144k m / h ¹ s totally erroneous. When the two mobile terminals move at a speed of 60 km / h, the additional location information according to the invention can therefore provide a gain of 15.32% compared to a symmetrical speed according to a TDMA scheme.

Even at a high speed 60 <V <144k m / h the invention makes it possible to obtain a sum flow greater than that obtained with orthogonal TDMA access. Taking into account the gain on the sum speed obtained with the invention, it is then possible for the operator to reduce the density of the relays or to put “off” (switch off) some of the relays which makes it possible to reduce energy expenditure or d 'infrastructure.

The curves in FIG. 7 represent the minimum density of relays required as a function of the speed for several values of symmetrical flow rate o ¹ (identical symmetrical flow rates for the different terminals). For example, with a symmetrical flow value d ¹ = f) 4 when the speed increases the minimum density of necessary relay increases.

FIG. 8 illustrates the structure of an access point BS which includes the server S according to an embodiment of the invention.

The simplified structure of a relay or a base station hosting a server S participating in the implementation of a transmission method according to the embodiments described above is described below and illustrated by Figure 8.

Such a relay or base station BS comprises an Rx / Tx transmitter / receiver for a wireless connection with a mobile terminal (terminal) and the server S which comprises a memory MEM comprising a buffer memory and a computer in the form for example of a processor μΡ controlled by a computer program Pg implementing the steps of the transmission method according to the invention.

[0141] The memory MEM stores at least the table of ^vectors after such an exhaustive search. The table is addressable by a combination (λ, Ts, ^v k, Rb) comprising the density λ of the relays, the time offset Ts, the average speed ^v k of displacement of the terminal k and the distance R b

The Rx / Tx transmitter / receiver makes it possible to receive messages transmitted from one or more mobile terminals and to transmit messages to one or more vehicles.

[0143]

[0144]

At initialization, the code instructions of the computer program Pg are for example loaded into the buffer memory before being executed by the processor μΡ. The processor μΡ implements the steps of the transmission method described above, according to the instructions of the computer program Pg.

To this end, the processor μΡ addresses the memory MEM with the combination (λ, T _s , ^v ft, R _B ) to obtain in return an estimate of the state A of the transmission channel tb between the relays and the terminal k to a current transmission interval tb - The processor knows the location g [tj, - T _s j of the terminal k via a feedback of

[0145]

[0146]

[0147]

[0148]

[0149]

[0150]

This terminal and this location is time-stamped with the value 1 _s . This feedback can possibly be transmitted between relays via a link, for example a wired link between relays.

The μΡ processor addresses the MEM memory to obtain the overall state

5.: = [5,. , ..., S,. ] real of the transmission channel between the relays and the terminals at a transmission interval earlier than the current transmission interval t _b , the real state may have been memorized following feedback from the terminals received by the Rx transmitter / receiver / Tx or transmitted via a link, for example wired between relays.

From the estimated state ç and the real state S, the processor μΡ determines the * tb values of the coefficients i, 2, ® 2 ^K '- 2 + ^and therefore the respective lengths of the different parts of the packet. data to be transmitted.

The processor μΡ selects the segments to be transmitted from the current signals V _b and the segments already transmitted V _kb knowing the estimated overall state of the transmission channel between the relays th and the terminals at this current interval and knowing the overall state

S,: = [5,. , ..., S,] real. The segments already transmitted tb-ι L 'x, t _b -i J ^{6 J}

V _{? <B} _ _I can be temporarily stored in the MEM memory before being possibly retransmitted.

The processor μΡ controls the Rx / Tx transmitter / receiver so that it codes with a certain yield a segment to be transmitted, so that it adapts the yield of the segments to be transmitted and so that it positions the coded segments of adapted yield in the different parts of the data packet to be transmitted.

The Rx / Tx transceiver transmits the data packets.

According to a preferred implementation, the steps of the method according to the invention are determined by the instructions of a program incorporated in an electronic circuit such as a chip itself which can be arranged in an electronic device such as a relay, a server or a station. based. The program can optionally be broken down into several modules which are distributed over several relays and / or base stations. The method according to the invention can just as easily be implemented when this program (or its modules) is loaded into a calculation unit such as a processor or equivalent, the operation of which is then controlled by the execution of the program.

Consequently, the invention also applies to a computer program (or its various modules), in particular a computer program on or in an information medium, suitable for implementing the invention. This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code such as in a partially compiled form, or in any other form desirable for implementing a method according to the invention.

The information medium can be any entity or device capable of storing the program. For example, the support may include a storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or else a magnetic recording means, for example a floppy disk or a disc. hard.

Alternatively, the information medium can be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the process in question.

On the other hand, the program can be translated into a transmissible form such as an electrical or optical signal, which can be routed via an electrical or optical cable, by radio or by other means. The program according to the invention can in particular be downloaded from a network of the Internet type.

List of documents cited

(Ref 1) T. Bai and R. W. Heath, “Coverage and rate analysis for millimeter-wave cellular networks,” IEEE Trans. Wireless Commun., Vol. 14, no. 2, pp. 1100-1114, Eeb. 2015

Annex A

[0157] [Tables 1]

etaSsigjla 1 binaifeà ) = (0 „0) 0 0 0- y J “(-1.-8} : .C5 ? 2, - i. * 1 S; ..,,) = (0..1) 0 0 0

Table 1

[0159]

[Paintings!]

Fl f ₂ f ₃ Fjj F13 F ₂₃ Fi ® Fa Fl ® V Fj B- v OGO 0 0 0 001 Fl Fa / 0 Fia 0; 0 ' 0 Fi F ₂ 010 Fi • Q ^: Fa 0 / F13 0; F. 0 ^: F>, Oil F < 0 ' 0 F _î2 F _{J: Ï} · 0 0 0 100 0 Fa Fv * 5 0 · 0 F ₂₃ f ₂ f ₃ 0 101 0 V 2 F12 0 f ₂₃ · $ 0 0 110 s 0; f ₃ 0 · F _h F.x 0 0 111 0 0 0 0: 0 0 '0 0 0

Table 2

Claims (1)

[Claim 1] Method (1) for transmitting data packets, the data coming from K messages intended respectively for K terminals (Cl, C2, .., CK), via at least a first millimeter band access network comprising relays (R) distributed in space according to a determined density λ or via a second access network of frequency bands lower than 6GHz comprising base stations (BS) called macro, such as a choice of the network d access is carried out before each transmission on the basis of a comparison between estimated bit rates with each of the access networks, the message M _k intended for the terminal k comprising B segments ^m k, i> · » ^m k, B coded in the form of binary signals ^v ki>, V _ktB , K> 2, k = 1, ... K, t _h = [1, ..., B + K-1], comprising for the various terminals: estimation of a state ^S k, t _b of a transmission channel between the relays (R) and the terminal k at a current transmission interval t _b knowing the density λ of the relays (R), a time-stamped location of the terminal k at an instant t _b - T _s prior to the current transmission interval t _b and an average speed ^v k of displacement of the terminal, the channel being considered of erasure type beyond a distance R β given around each relay (R) and comprising: at the current transmission interval, transmission of data selected from the current binary signals V and the already transmitted binary signals V _kh _ ₁ knowing the overall state £ Λ Λ, ..., 57 L th -k, estimated of the transmission channel between the relays and the terminals at this current interval and knowing the overall state: = [S ', _,. 1 real channel tb-ι LL% -1 transmission between relays and terminals at a transmission interval prior to the current transmission interval ^f b [Claim 2] Method (1) of transmission according to claim 1, according to which them data to be transmitted are in a data packet and the packet includes at most 2 ^ _ 2 + cf; Pities whose respective lengths are in ratios & 1, 2> OL ₂ ^K - 2 + Cg of the length of the bundle with (X _r) K ,,, ..2 = 1 - (X 1 - Ct n - .. . - (X .-. K ...,., 2 ,, according to 2 - 2 + C _E ¹ 2-2 + C ^ - the coding efficiency of a binary signal to be transmitted at the interval current transmission is adapted to be transmitted in one of the parts of the packet, the values of the coefficients being determined as a function of the estimated and real states of the transmission channel to obtain an optimal sum rate. [Claim 3] Transmission method (1) according to claim 2, according to which the determination of the maximum sum rate is obtained by an exhaustive search during which the sum rate is calculated for different combinations of the values of the coefficients. [Claim 4] Transmission method (1) according to one of claims 2 and 3, according to which the packet can comprise K first parts reserved for current binary signals. [Claim 5] Transmission method (1) according to one of claims 2 to 4, according to which the packet can comprise a last part reserved for binary signals already transmitted at a previous transmission interval, a _E e [O, l], z = [l ..... 2 ^K - 2 + cf]. [Claim 6] Transmission method (1) according to one of claims 2 to 5, according to which the package may include parts reserved for pairs of common binary signals. [Claim 7] Transmission method (1) according to the preceding claim, according to which a combination of binary signals is a bit-to-bit binary addition of two current binary signals. [Claim 8] Transmission method (1) according to one of the preceding claims, according to which the state of the transmission channel between the relays and a terminal is determined by taking into account a return from the terminal on reception of transmitted data. [Claim 9] Server (S) which can be hosted in an access point of a first millimeter band access network comprising access points (R) distributed in space according to a determined density λ or of a second network d frequency band access below 6 GHz including so-called macro access points (BS), for transmitting data packets, such that a choice of access network is made before each transmission on the basis of a comparison between estimated bit rates with each of the access networks, the data coming from K messages intended respectively for K terminals, the message M g intended for the terminal k comprising B segments ^m k, i '' ^m k, B coded in the form of binary signals V _fcl , ..., V _kB , K> 2, k = l, ... K, t _h = [l, ..., B + K-1 \, including: a computer (μΡ) to estimate a state ç of a channel of k, t _b transmission between the relays and a terminal k among the K terminals at a current transmission interval tb knowing the density λ of the relays (R), a location of the terminal k at an instant ΐ _b - T _s prior to the current transmission interval t _b and an average speed ^v k of movement of the terminal, the channel being considered of the erasure type beyond a given distance R b around each relay, a computer (μΡ) to select data to be transmitted in a packet, among the current binary signals V _k and the binary signals already transmitted V _kb _ ₁ knowing the estimated overall state of the transmission channel between the relays and the terminals at this current interval and knowing the global state S \: = [S ',, .... S. ] real of the transmission channel between the relays (R) and the terminals (C1, C2, ..., CK) at a transmission interval earlier than the current transmission interval t _b [Claim 10] Telecommunication system comprising at least a first millimeter band access network comprising access points (R) distributed in space according to a determined density λ and a second band access network having frequencies below 6 GHz comprising so-called macro access points (BS) characterized in that it comprises a server (S) according to claim 9. Computer program on an information medium, said program [Claim 11] comprising program instructions adapted to the implementation of a transmission method according to any one of claims 1 to 8, when said program is loaded and executed in a communication entity intended to implement the transmission method. [Claim 12] Information carrier comprising program instructions suitable for implementing a transmission method according to any one of claims 1 to 8, when said program is loaded and executed in a communication entity intended for implement the transmission process.