Apparatus and method for analyzing performance of a mobile network

FIELD OF THE INVENTION

[0001] The present invention relates to network simulation and more particularly to simulated performance analysis of a large-scale mobile network.

BACKGROUND OF THE INVENTION

[0002] Network simulation systems provide convenient and effective tools for analyzing network performance. Simulation is employed for rapid prototyping of network topology, and for network performance analysis under simulated operating conditions.

[0003] A typical simulation system provides better results when it is customized for a specific network design. Important considerations in designing a simulation system are the underlying network size, component characteristics, and operational parameters. Many network applications involving defense communications, distribution tracking systems, etc., require large scale mobile networks with high bandwidth and throughput. Such networks are generally custom designed and require specialized and application specific simulation systems.

[0004] Modern approaches to mobile network design employ performance enhancing architectures. For example, architectures like TDMA and CDMA multiplex the data channel to achieve high data rates. Large scale networks having performance enhancing architectures and significant inter-node distance need improved simulators.

[0005] Accordingly, there is a need for a simulation system and method designed for a large scale mobile network. More specifically there is a need for such a simulation system and method capable of simulating high speed data transfer among distant scattered nodes. A further need exists to output the results of the simulation system and method in a user friendly manner.

SUMMARY OF THE INVENTION

[0006] The present invention is directed to a simulation system for a mobile communication network. In a preferred form the network simulates multiple nodes which are interconnected by synchronous and TDMA links. The nodes have phased array antennas for communicating among the nodes. At the start of simulation, the nodes, synchronous links and TDMA links are initialized by appropriate controllers. Some of the synchronous and TDMA links are censored, i.e. eliminated, to avoid network self-interference. A user specified data-traffic model is stored in a memory associated with the simulation system. The stored data-traffic model is applied to the simulated network. Network traffic is then analyzed for the stored data-traffic model and selected network parameters are calculated. Thereafter, the parameters are outputted through an output device. A variety of output devices including a display device can be effectively employed for outputting network parameters.

[0007] In one of the preferred embodiments of the invention a link censor is employed to avoid self-interference in the synchronous and TDMA links. In another embodiment the synchronous link controller initializes and manages the synchronous links; the TDMA link controller initializes and manages the TDMA links.

[0008] In one of the preferred embodiments the invention is implemented as a computer program. Another preferred embodiment implements the invention in a hardware system. Yet another preferred embodiment implements the invention as a combination of hardware and software elements.

[0009] In a preferred embodiment the network analyzer performs the required network analysis and computing performance parameters. In another preferred embodiment the user specified data traffic model is customizable by the user.

[0010] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0012]FIG. 1 is a block diagram representing a simulation system in accordance with a preferred embodiment of the present invention;

[0013]FIG. 2 is a block diagram of a simulated phased array antenna;

[0014]FIG. 3 is a representation of the slotting latency; and

[0015]FIG. 4 is a flow-chart showing the operational steps of the simulation system shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0017] Referring to FIG. 1, there is shown a simulation system <b>10</b> in accordance with a preferred embodiment of the present invention. The simulation system <b>10</b> consists of a simulated network <b>12</b> having simulated nodes <b>14</b> interconnected by synchronous communication links <b>16</b> and TDMA (Time Division Multiple Access) communication links <b>18</b>. A synchronous link controller <b>20</b> is used to set up initial parameters for the synchronous links <b>18</b>. A TDMA link controller <b>22</b> is used to set up the initial parameters for the TDMA links <b>18</b>. The synchronous links <b>16</b> serve to provide synchronous communication channels among the simulated nodes <b>14</b>. A link censor <b>24</b> simulates link censoring to avoid self-interference for synchronous links <b>16</b> and TDMA links <b>18</b>.

[0018] The simulated nodes <b>14</b> are the basic building blocks of the simulation system <b>10</b>. Simulated nodes <b>14</b> are the sources and sinks of the communications traffic in the network <b>12</b>. The inter-node data-rate between any two of the simulated nodes <b>14</b> at a given instance is preferably about 100 Mbps. The distance between any two of the simulated nodes <b>14</b> having direct links could be up to 900 km, or possibly even longer.

[0019] High network data communication rates are possible with the use of directional antennas, and in particular with phased array antennas (“PAAs”). One or more phased array antennas <b>34</b> are located on each of the simulated nodes <b>14</b>. The systems based on antennas <b>34</b> have the ability to hop a beam from target to target as rapidly as 10,000 times per second, and the ability to form spatially narrow beams that reduce self-interference within the network. The node controller <b>36</b> sets the location, orientation, and velocity vector of each simulated node <b>14</b> and the relative location and orientation of each simulated antenna <b>34</b> on each simulated node <b>14</b>.

[0020] Referring to FIG. 2, the antennas <b>34</b> have a PAA orientation storage medium <b>38</b> for storing information about the orientation of a particular antenna <b>34</b> relative to its node platform axes. A node orientation locator <b>40</b> ascertains the orientation in space for each of the simulated nodes <b>14</b>. A PAA absolute orientation calculator <b>42</b> calculates the absolute orientation for each of the antennas <b>34</b>. The PAA absolute orientation calculator <b>42</b> performs the calculations for absolute orientation based on the absolute orientation of a specific simulated node <b>14</b> and relative orientation of each of the antenna <b>34</b> relative to that specific simulated node <b>14</b>. A PAA “field-of-regard” finder <b>44</b> locates the antenna <b>34</b> on a given simulated node <b>14</b> having other simulated nodes <b>14</b> within its field-of-regard. A PAA scan angle calculator <b>46</b> computes the scan angle at which an antenna <b>34</b> must operate to point its beam at a particular simulated node <b>14</b>. An antenna gain calculator <b>48</b> computes the antenna gain of a selected antenna <b>34</b> in the direction of one of the simulated nodes <b>14</b>, where that simulated node <b>14</b> is not the target of the beam of the selected antenna <b>34</b>.

[0021] With further reference to FIG. 1, TDMA links <b>18</b> provide TDMA communication channels between the simulated nodes <b>14</b>. The TDMA links include time slots <b>52</b>. The TDMA links <b>18</b> further comprise beam-hopping TDMA type links. The node controller <b>36</b> simulates the process by which a simulated node <b>14</b> discovers its neighboring simulated nodes <b>14</b> as well as attributes of those neighboring simulated nodes <b>14</b>. The TDMA link controller <b>22</b> executes computations used by the simulated node <b>14</b> to select the TDMA links <b>18</b> to form with the other simulated nodes <b>14</b>, and the initial slots <b>52</b> to use in each of the TDMA links <b>18</b> to be formed. The controller <b>22</b> controls the number of slots <b>52</b> by adding or decreasing the number of slots <b>52</b> as the traffic increases or decreases. The controller <b>22</b> initiates a mechanism to transmit link negotiation messages and slot negotiation messages between the simulated nodes <b>14</b>.

[0022] At the start of simulation, the synchronous link controller <b>20</b> sets up initial parameters for the synchronous links <b>16</b>. The controller <b>20</b> executes computations that a given simulated node <b>14</b> uses to select the proper synchronous links to form. The controller <b>20</b> initiates a mechanism to transmit link negotiation messages.

[0023] The link censor <b>24</b> computes the estimated interference likely to be caused by the proposed links to be formed. The link censor <b>24</b> simulates the propagation of location data and frequency assignment data among all the simulated nodes <b>14</b>. The link censor <b>24</b> uses the location data together with data from the antenna gain calculator <b>48</b> to determine which of the proposed links will cause unacceptable interference with other links, and then censors, or blocks, formation of the proposed links that cause unacceptable interference.

[0024] A data traffic model <b>28</b> is specified by the user and is used to simulate the operational environment for the network <b>12</b>. The model <b>28</b> is stored in a memory <b>26</b>. To form the model <b>28</b>, the user specifies the quantity of data moving from the simulated nodes <b>14</b> functioning as sources to the other simulated nodes <b>14</b> functioning as sinks. The user further specifies a routing protocol at each of the simulated nodes <b>14</b> for determining the needed relay simulated nodes <b>14</b> for data streams starting from the simulated nodes <b>14</b> functioning as sources to the other simulated nodes <b>14</b> functioning as sinks. The model <b>28</b> is applied to the network <b>12</b> to form a simulation of a network operating under the operational environment specified by the model <b>28</b>.

[0025] With further reference to FIG. 1, a network analyzer <b>30</b> analyzes the network traffic after the model <b>28</b> is applied to the network <b>12</b>. The network analyzer <b>30</b> also computes the required network parameters. The network analyzer <b>30</b> then sums all data volumes from the bytes and packets that are assigned by a user specified routing protocol to each of the simulated nodes <b>14</b> and flowing in each direction along the synchronous links <b>16</b> and TDMA links <b>18</b>. The network analyzer <b>30</b> also computes the total interference for each of the synchronous links <b>16</b> and the TDMA links <b>18</b>.

[0026] The network analyzer <b>30</b> further computes the total latency, including the slotting latency, for each route in the network, wherein a given route comprises at least a pair of simulated nodes <b>14</b> and one or more interconnecting synchronous links <b>16</b> or TDMA links <b>18</b>. The network analyzer <b>30</b> computes the average (and/or worst case) slotting latency for each of the TDMA links <b>18</b>, the sum of slotting latencies for all the TDMA links <b>18</b> and synchronous links <b>16</b> along each route and the sum of total latencies for all TDMA links <b>18</b> along each route. The data traffic model <b>28</b> is configurable by the user to set the processing delay by providing a user defined function in the software. Such a user defined function can be constant for all the simulated nodes <b>14</b> or may be a function of traffic load and/or hardware on each of the simulated nodes <b>14</b>.

[0027] Referring to FIG. 3, the slotting latency is the delay between a message reaching the top of the transmit queue for the TDMA link <b>18</b> and the beginning of the next outgoing burst for that TDMA link <b>18</b>. For example, if the message in the transmit queue of a TDMA link reaches the top of its transmit queue at top <b>60</b>, i.e., midway within slot number <b>5</b> (approximately at the 4.4 slot position), then it cannot be transmitted until the beginning of slot number <b>10</b>, assuming that that the next burst for the TDMA link begins at slot number <b>10</b>. The slotting delay is calculated as the product of 4.6 and slot duration <b>54</b>. The average slotting latency for a link is the length of a TDMA cycle divided by the number of slots allocated to that link in each cycle. Total latency for each route is the sum of slotting latency along every link in the route, time of flight along every link in the route, and the processing delay at every one of the simulated nodes <b>14</b> in the route.

[0028] The network analyzer <b>30</b> determines the actual PAA beam pattern for each of the synchronous links <b>16</b> and the TDMA links <b>18</b> used in the network <b>12</b>. The network analyzer <b>30</b> sums all the interference arriving at the receive end of each of the synchronous links <b>16</b> and the TDMA links <b>18</b> from every antenna <b>34</b> on the simulated nodes <b>14</b> located above the radio horizon. For the TDMA links <b>18</b>, the time-of-flight information is used to compute the maximum total interference arriving during each slot <b>52</b> used by each of the TDMA links <b>18</b>. The network analyzer <b>30</b> further determines the carrier signal strength at the receive end of the TDMA links <b>18</b> and computes the carrier to interference ratio for each of the TDMA links <b>18</b>.

[0029] The network analyzer <b>30</b> generates selected parameters for output which are transmitted to an output mechanism <b>32</b>. In a particular embodiment, the attributes of each of the synchronous links <b>16</b> and the TDMA links <b>18</b> may be shown in a color coded two-dimensional or three dimensional representation. Other color coding or graphical representation for the output could be as follows:

[0030] (1) Each of the synchronous links <b>16</b> and TDMA links <b>18</b> could be shown as a line connecting two points on a display, where the two points represent the spatial location of two of the simulated nodes <b>14</b>. For bi-directional synchronous links <b>16</b> or TDMA links <b>18</b> (most of which are bi-directional), two adjacent lines could be used, one representing each direction of the link.

[0031] (2) Encoding color, brightness, and/or width of each line to represent the value of any of the following: link frequency, link capacity, link data rate (absolute rate), link data load (rate relative to the capacity), interference (relative to the limit for that link), latency. For example, acceptable values of link load might be encoded as shades of blue, where the brighter blue represents higher loads, while loads exceeding the capacity might be encoded as shades of red with brighter red representing higher levels of overload.

[0032] (3) Facility to let the user specify which link attribute to display as above. For example the user could specify that color be used to indicate data load instead of using color to indicate frequency.

[0033] (4) Encoding each line as a series of dashes representing the TDMA slots <b>52</b> used by that link, with each dash showing the size and location of a burst at a particular moment in time.

[0034] (5) Turning off the display of all synchronous links <b>16</b> and TDMA links <b>18</b> except those belonging to a user specified frequency band for clarity in understanding the interference situations.

[0035] (6) Displaying the radio horizon of each of the simulated nodes <b>14</b> with horizon indicators shaped as circles centered on the locations of the simulated nodes <b>14</b>, where the circle indicates the farthest location at which a receiver on the ground could receive a signal from the a given simulated node <b>14</b>. This horizon indicator could help the user in understanding the interference data. When the radio horizon of two of the simulated nodes <b>14</b> touch or overlap, then those two of the simulated nodes <b>14</b> will be in radio-line-of-sight, i.e., they will be able to form a link to each other (with power permitting) and/or interfere with each other's reception of links from other simulated nodes <b>14</b>. In a two dimensional map type display, the horizon circle would also indicate the altitude of the node. At higher altitudes the horizon circle would have a larger diameter.

[0036] Referring now to FIG. 4, the method of the present invention will be described. The method involves initializing the PAA equipped nodes <b>14</b> by defining their locations, orientations, and velocity vectors as indicated in step <b>56</b>. A loop is initiated, as shown in step <b>58</b>, to check whether any more links are to be formed. If any more links are to be formed, the process proceeds from step <b>58</b> to step <b>60</b>, otherwise the process jumps to step <b>70</b>. The type of the next link to be formed is checked in step <b>60</b>. If the next link to be formed is the TDMA link <b>18</b> the process branches further to step <b>62</b> otherwise to step <b>64</b> for forming the synchronous link <b>16</b>. As indicated in step 2, the TDMA link <b>18</b> is proposed and the slots <b>52</b> are negotiated. At step <b>66</b>, depending upon whether the proposed TDMA link <b>18</b> interferes with other links, that TDMA link <b>18</b> is either censored or is formed. Similarly, synchronous link <b>16</b> is proposed at step <b>64</b>, and further in step <b>68</b>, depending upon whether the proposed synchronous link <b>16</b> interferes with other links, the proposed synchronous link <b>16</b> is either censored or is formed. The user specified data traffic model <b>28</b> is next applied to the simulated network <b>12</b> in step <b>70</b>. Necessary computations for the total traffic passing through each of the nodes <b>14</b>, synchronous links <b>16</b> and TDMA links <b>18</b> is then performed, as shown in step <b>72</b>. The desired output is generated as the final operation in step <b>74</b>.

[0037] The present invention thus provides a system and method for simulating a large scale mobile network having the simulated nodes <b>14</b> thereof connected by synchronous links <b>16</b> and TDMA links <b>18</b> generated by applying a user specified data traffic model <b>28</b> to the simulated network <b>12</b>. The simulated nodes <b>14</b> have phased array antennas <b>34</b> for communicating with the other simulated nodes <b>14</b>.

[0038] In one of the preferred embodiments the invention is implemented as a software computer program. Another preferred embodiment implements the invention in a hardware system. While, another preferred embodiment implements the invention as a combination of hardware and software elements. Those skilled in the art will appreciate that the invention is not limited by the implementation components or methods as a invention is capable of being embodied in a variety of ways.

[0039] The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.