Connectivity with mobile objects
Last updated
Last updated
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This document describes the ability of the Astra Wireless devices to provide sustainable wireless connectivity with mobile objects in various scenarios. A basic deployment is generally presented along with the features related to its implementation for the mining industry, railway and water transport.
Let's look at the scenario below (Figure 1), which involves the movement of one or more objects throughout the enterprise area along a given path between points A and B. The network control center is located at a certain distance from the area where the moving object can be located.
The project goal is to organize a reliable wireless connectivity between the control center and the mobile objects in order to provide various information services, such as telemetry data gathering, video surveillance, telephony etc.
Two categories of tasks must be solved to achieve this goal:
Network deployment including the following sections:
A backhaul radio network. The coverage of the backhaul radio network should correspond to the object's area of motion.
An aggregation node. The aggregation node is designed to collect the traffic of the backhaul radio network devices and it is a gateway between the radio network and the enterprise network.
A backbone link between the aggregation node and the control center.
Fault tolerance and roaming capabilities for:
Ensuring the link fault tolerance at the access level (backhauling).
Providing seamless subscriber roaming within the backhaul radio network.
Ensuring fault tolerance of the main link between the aggregation node and the control center.
Ensuring the possibility of implementing QoS policies.
The solution to the tasks described above is shown in Figure 2 and it can be divided into four components:
The backbone link towards the enterprise network
The aggregation node
A backhaul radio network
The object's area of motion
The backhaul radio network consists of several base stations (BS), joined by a wired infrastructure. Each BS can consist of one or several sectors and the combination of their antenna patterns forms the radio network coverage area. The Astra Evolution families devices can be used as CPEs and BS sectors. Keep in mind that wireless links as well as combined infrastructure can be used to join several BSs.
The base stations are joined at the aggregation node where the AstraMUX device is installed. As shown below, the AstraMUX simplifies the configuration for the Astra devices by joining all the BSs into a single MINT area.
A backbone link is established between the aggregation node and the network control center. The choice of specific devices for the radio link is determined by the transmitted traffic capacity. The following throughput values can be achieved:
Evolution family devices: up to 800 Mbps.
Quanta 4 / 5 / 6 devices: up to 650 Mbps.
Quasar family devices: up to 2100 Mbps.
A subscriber station (CPE) is installed on each mobile object and its configuration contains radio profiles f or each BS sector in its area of motion. The operational principle is that the CPE can switch the connections while moving between the base stations. Since the BS sectors provide coverage for the entire area in which the CPE can be located, the CPE is always in the coverage area of at least one BS. As soon as the radio parameters of the current connection deteriorate, the CPE interrupts the radio link and connects to another sector. So, while the object moves from point A to point B (Figure 2) the CPE is connecting one by one to the sectors of BS1, BS2, BS3 and BS4.
Keep in mind that the CPE cannot be simultaneously connected to two base stations, because the device has one radio module, so the roaming between the base station sectors is accompanied by a short-term connectivity break. Several CPEs can be simultaneously connected to one BS sector.
In addition to the infrastructure described earlier there is an extended list of requirements, which make the solution fault-tolerant and more efficient:
The link fault tolerance at the access level is ensured by overlapping the sectors' radiation patterns at the backhaul radio network design stage. So, if there is more than 50% overlapping with the neighboring sectors, a failure in one of the sectors will not affect the coverage area of the radio network. Radio frequency planning requires a complex approach and it is discussed in more detail in the following sections.
As noted, roaming in the proposed solution is not seamless, because the roaming between different base stations is accompanied by a connectivity break. A seamless roaming requires the installation of a second CPE device on each moving object. Such a solution is described below.
Astra Wireless devices can be used in various scenarios of point-to-point link reservation and aggregation. For example, the backbone link can be reserved using the proprietary failover technology which requires the installation of a second backup wireless link. Failover allows automatic reservation of the backbone link using only one frequency channel. The options for organizing link reservation are presented in the Link aggregation, balancing and redundancy document.
The implementation of a QoS policy does not require the installation of additional devices and it is solved by configuring the wireless units and the AstraMUX device:
The telemetry gathering service, telephony and remote control are sensitive to delay and jitter, so they require careful configuration of traffic distribution rules by classes. A low jitter for sensitive services can be achieved by using software versions with TDMA technology support on the Evolution devices.
The video surveillance service, in addition to the delay requirements, demands an increased throughput in uplink (from the CPE to the BS). The Evolution devices support the time division multiple access method (TDMA), which allows a flexible allocation of the available throughput between the upstream and downstream channels.
Using a single infrastructure to provide a range of different services requires flexible allocation of the available throughput.
Each implemented solution is unique and requires careful preliminary planning. It is a very important stage, saving resources at the design stage can greatly increase the operational costs. Within this document, the radio frequency planning and placement of the devices will be reviewed.
Frequency planning is a complex, creative process that defines:
The installation coordinates.
The suspension height, azimuth and antenna elevation.
The part numbers of the devices.
The frequency channels and the transmission power.
The result of the frequency planning is a device allocation map with basic radio settings. A convenient tool for radio planning and potential performance assessment depending on the radio parameterscould be found on the https://astrawireless.net/.
The frequency channel selection is determined by the following factors:
Regulatory restrictions: RF regulation is determined at the legislative level. Usually, it is allocated either a frequency range that is allowed for free use with certain restrictions(radiated power, antenna suspension height etc.) or a frequency range for which the permission must be obtained.
Radio module capabilities: the radio module of the wireless devices supports a limited set of emission frequencies and this should be taken into account at the design stage.
Physical features of the electromagnetic waves propagation: propagation distance, the effect of precipitation and interaction with obstacles are determined by the electromagnetic wave frequency, which must be kept in mind during preliminary calculations.
The interference level: the operation of third-party wireless devices has a significant impact on the system's performance, so it should be taken into account when designing the link. The interference level is affected by the radiated power and by the frequency channels used by the third-party devices operating in the same area. In addition to interference from third-party devices, the neighboring sectors can have influence on each other. The reducing of the interference between your own devices can be achieved by using different frequency channels. Particular attention should be paid to the frequency channel selection in projects with multisector configurations in order to minimize the influence of the BS sectors on each other.
Some frequency allocation examples are presented below. Figure 3a illustrates a scheme where each BS sector has it's own frequency channel. This approach requires the allocation of 4 frequency channels.
Let's look at the optimized scheme (Figure 3b). Since the sectors' position is chosen in such a way that the radiation patterns of BS1 and BS3, BS2 and BS4 do not intersect in pairs, they will not interfere with each other. This will optimize the frequency resource utilization, reducing the number of frequency channels from 4 to 2.
The position of the devices in space determines the actual quality indicators of the wireless link. The position of the devices is determined by the:
Installation coordinates.
Azimuth and antenna elevation.
Suspension height.
In projects with mobile objects, the antenna's directional properties should be taken into account. If the BSs are static and the radio coverage area is constant, then the CPE's antenna radiation pattern can greatly affect the link quality. Astra Wireless product portfolio includes devices with integrated antennas and the ability to connect external antennas as well. The selection of a specific device is determined by the specific requirements of the project.
The route profile must be evaluated along the entire trajectory of the object. This will allow to find potential "dead zones", with no connectivity with the mobile object. A decision to change the location of several base stations might be necessary in this case. In addition, perform a survey along the enterprise's territory, because the link planning tool does not take into account the effects of obstacles such as trees, buildings etc.
The Astra Wireless product portfolio includes a wide range of accessories, including mounting kits that allow to install devices in various conditions with the possibility of flexible alignment and the CAB-RV1 alignment tool which allows to perform preliminary device diagnostics.
The Ethernet link layer protocol was developed for the wired networks and does not take into account the specifics of the wireless environment. Wireless device manufacturers can use standard wireless protocols, such as Wi-Fi, or use their self-developed protocols. Astra Wireless has developed a proprietary data transfer protocol called MINT, especially designed for data exchange in a wireless environment.
MINT (Mesh Interconnection Network Technolohy) - Astra Wireless proprietary technology used by the Evolution family devices, provides data transfer between devices via wireless and wired links.
One of the MINT protocol's main concepts is the MINT area. A MINT area consist of many neighboring devices and data exchange between them is carried out using MINT frames.
Let's look at the solution described below, that implements the MINT areas concept (see Figure 4). A radio link is installed between the Master and Slave devices, they form MINT 5 area. Each of the BS1, BS2, BS3, and BS4 sectors is potentially ready to establish a radio link with the CPE installed on the mobile object and form a separate MINT area with the corresponding identifier.
Note that the MINT protocol is intended for data exchange within the MINT area. Data outside the MINT area can be transmitted using other protocols, such as Ethernet, i.e. the CPEs and each of the base stations are the gateway between the MINT and Ethernet networks. In our scheme, data is exchanged between a mobile object and a control center, i.e. the frame will go through several Ethernet segments and MINT areas in the forward and backward directions. Thus, switch group configuration on each device is a prerequisite for data transfer.
Switch group configuration example:
In addition to encapsulating the Ethernet frames during the transmission through the MINT area, the MINT protocol performs an exchange of service messages to fill in the frame redirection table. The frame redirection table allows to select the frame transmission route through the MINT area in accordance with the radio parameters and the link load. This mechanism guarantees the selection of the route with the optimal radio parameters and prevents loops.
If necessary, you can influence the path selection algorithm by setting the link metric value manually. This can be done by summing the calculated and additional costs or by fixing a certain value.
Setting the additional and calculated values:
Setting the fixed value:
Data transfer and QoS configuration on each wireless device is a time-consuming task that can be simplified by extending the MINT area. The schemes intended to simplify the configuration of the wireless devices by joining them into a single MINT area, are shown below.
The main disadvantage of the solution above is the necessity to configure switch groups on all wireless devices. Since the switch group is a gateway between MINT and Ethernet, it is possible to combine all the BSs of the radio network into a single MINT area, transferring the gateway role to the AstraMUX switch (see Figure 5). In this case, a switch group has to be configured only on the AstraMUX.
Using the MINT protocol in a wired infrastructure is possible with the help of the PRF (pseudo radio) interface. It is a virtual interface that has a wired interface as parent and it encapsulates Ethernet frames into MINT frames. Configuration via CLI:
Create a PRF interface on a wireless device or on the AstraMUX:
Join RF and PRF interfaces on the wireless device:
Join two PRF interfaces on the AstraMUX:
The advantages of such a solution is the simplification of the QoS configuration, as traffic processing rules for different service classes are configured only on the AstraMUX.
The disadvantage of the scheme having the backhaul radio network devices joined into a single MINT area is the quality of service policy that needs to be implemented at the backbone devices as well: the traffic classification rules must be duplicated on the AstraMUX and on the Master and Slave devices. If these rules are not duplicated, the effect of the QoS policy implementation can be significantly reduced.
One of the solutions is to combine the devices of the backbone link into a single area with all the other devices (see Figure 6). This solution is possible only when using Evolition family devices for the backbone link. In this case, the unified traffic classification rules configured on the Master device will be valid in the entire MINT area. In addition, the gateway functions between MINT and Ethernet can be transferred to the Master device, while any switch can be used instead of AstraMUX.
The movement of the mobile object, with the CPE installed on top, within the access radio network is accompanied by a transition from the coverage area of one BS sector to another sector's coverage area of the same or of another BS. The transition process of the CPE between the BS sectors is called roaming. Roaming implies the disconnection of the radio link with the first sector and the connection establishment with the second sector.
Let's look at the roaming mechanism:
There is a radio link between the CPE and BS1.
The vehicle moves and the radio link between CPE and BS1 becomes unavailable. The reason is the inability to maintain the communication due to insufficient signal power. As it is shown below, the initiator of the radio link disconnection can be either the CPE or the corresponding sector of BS1.
The CPE is trying to reconnect to BS1. If successful, the algorithm returns to step 1; if not - to step 4.
The CPE searches for devices to establish the radio connection.
The CPE finds out BS2 and tries to establish a connection with it.
The CPE establishes a radio link with BS2.
A radio link can be established between two devices if the following requirements are met:
At least one of the devices has a Master role. Possible connections: Master-Master, Master-Slave. The solution architecture implies the configuration of the BS sectors as Masters and of the CPEs as Slaves.
A radio profile has been created in the CPE configuration, corresponding to the radio settings of the BS.
The signal parameters (RSSI, SNR, etc.) allow the data exchange at least at the minimal modulation.
On Master devices, only one set of radio parameters can be configured, which will be used to establish the links. On Slave devices, several radio profiles can be created, or only one, but with the ability to automatically select a frequency. Configuration via CLI:
Configure the radio parameters on the Master device:
Create a radio profile on the Slave device with a fixed frequency value:
Create a radio profile on the Slave device with automatic frequency selection (if a profile with a fixed frequency value is used, the command below will not be executed):
When the Slave device tries to establish a connection, it cyclicaly looks over the radio profiles added to its configuration. As soon as one of the profiles becomes suitable for link establishment with the Master device, it initiates the connection and the profile search is stopped. In case that a profile with automatic frequency selection is used, the Slave device tries to establish a connection with the Master by searching through the frequencies supported by the radio module. The list of frequencies to search through may be limited by the configuration of the user frequency grid.
Example of a custom frequency grid configuration via CLI (for the rf6.0 interface, the frequency range from 5000 MHz to 5100 MHz with a step of 10 MHz is set, when using a channel width of 20 MHz):
Obviously, link establishing can be a longtime operation when the automatic frequency selection mode is used due to the wide range of frequencies supported by the radio module. It is unacceptable in scenarios with roaming, therefore, we recommend to create on the CPE separate radio profiles for each BS sector of the backhauling radio network.
Master devices as well as Slave devices, support the dynamic frequency selection (DFS) mode. Before selecting a frequency, the devices with DFS support scan the available frequency range, evaluate the interference level and the presence of radar. The operational channel is selected among the channels free of radar, having a minimum interference level.
DFS is a standard technology for wireless devices, but the disadvantage is that the assessment of the radio environment is performed only in the beginning and no updates are performed during operation. Using an additional radio module, on some models of Astra Wireless devices, allows to implement the proprietary Instant DFS technology. An additional radio module constantly scans the air, performing a swap between frequency channels in accordance with the interference levels in real time. The DFS, Radar detection and Instant DFS technologies are described in the Dynamic Frequency Selection document.
DFS configuration via CLI:
Enable DFS on the Master device:
Enable DFS and Radar detection on the Master device:
Enable the iDFS support on the Master and Slave devices:
In this document frequency roaming represents a change in the operating frequency of the link, i.e. the frequency change is performed on both devices.
The frequency roaming mechanism operation is closely related to the Instant DFS function. When a frequency channel with a lower interference level is detected, the BS sector in PtMP mode or the Master in PtP mode must change the operating frequency. At the same time, the devices connected to them must also change the frequency channel. The behavior during frequency roaming is determined by the "roaming" parameter value:
leader: the device sets a new frequency channel and sends service messages to other devices to change their operating frequency as well. We recommend to configure this function on a device with the DFS / iDFS function enabled.
enable: the device, having received a command to change the operating frequency from the "leader", performs the transition to a new frequency channel.
disable: the device, having received a command to change the operating frequency from the "leader", ignores it.
This solution does not use the DFS technology, however, in projects where the use of DFS / iDFS is necessary, it is advisable to configure the BS sectors as "roaming leader" and the CPEs as "roaming enable".
Configuration via CLI:
Enable roaming on the Master device:
Enable roaming on the Slave device:
Restart the rf5.0 interface on both devices:
Note that a Slave device with "roaming enable", having received a command to change the operating frequency from the "roaming leader", will switch to another frequency channel even if there is no corresponding radio profile in the Slave device configuration. In this case, after a reboot, the slave will not be able to establish a link, because it will still be guided by the set of radio profiles added to the configuration.
The main disadvantage of the roaming mechanism: The CPE tries to keep the connection with BS1 until the signal is completely lost, and only then starts searching for other BSs to establish a new connection. Astra Wireless devices support the proprietary MultiBS function, which speeds up this process.
The roaming mechanism with the MultiBS function is presented below:
The link is established between BS1 and the CPE.
The vehicle moves and the radio link parameters between the CPE and BS1 deteriorate. The CPE interrupts the connection with BS1. Despite the fact that the radio link between the CPE and BS1 can be used to transmit data, the CPE notices a negative trend and preventively breaks the connection.
The CPE searches for devices to establish a connection.
The CPE senses one of the sectors on BS2 and tries to establish a link with this device.
The CPE establishes a radio link with one of the BS2 sectors.
Run the following command to enable the MultiBS function:
Let's look at a scenario in which the wired connection between the AstraMUX and the power injector of BS1 is damaged (see Figure 7), i.e. power is supplied to BS1 and the device is ready to establish radio connections, but data can not be transmitted to the control center.
The vehicle with the CPE installed starts moving along the trajectory, from point A to point B. Being in the BS1 coverage area, the CPE establishes a radio link with it. Since the wired connection is damaged, no data is transmitted between the moving object and the control center. Moving along the trajectory, the mobile object gets in the area where it is possible to connect to BS2, but the connection parameters with BS1 are satisfactory and the CPE does not perform roaming between the BSs. Without the MultiBS function, the CPE will keep the connection with BS1 until it leaves its radio coverage area.
The "Global" proprietary feature avoids this situation. If the Global function is activated on the CPE, it will only establish a radio link with the devices on which the Global function is also enabled. In addition, devices in the same MINT area can perform a proxy function for devices with the Global function enabled. Thus, if the Global function is enabled on the AstraMUX and on the CPE, then all the BSs will inform the CPE that they have a connection with the AstraMUX with the Global function activated at the time the radio connection is established. If a wired connection is damaged between BS1 and the AstraMUX, BS1 will not inform the CPE about the availability of the AstraMUX, i.e. the CPE will not establish a radio link with BS1.
Using the Global function allows to increase the fault tolerance of the backhaul radio network, however, it will have a positive effect only with an appropriate radio frequency planning since the coverage areas of the sectors must overlap.
Device configuration via CLI:
Enable the Global function on the CPE:
Enable the Global function on the AstraMUX:
One of the mechanisms to determine the moment of disconnection from one sector and the establishment of a connection with another, is the assessment of the SNR threshold values. Two thresholds are used in a wireless device configuration:
hiamp: minimum SNR value required to establish a radio link between two devices.
loamp: minimum SNR value at which the radio link between devices will not be broken.
Thus, the thresholds values' configuration on the BS or on the CPE is the mechanism for controlling the roaming process.
The SNR level configuration for establishing a radio link on wireless devices is performed using the following commands:
Configuration of minimum SNR value required to establish a radio link:
Configuration of minimum SNR value at which the radio link will not be broken:
One of the factors affecting the link parameters for a moving object is the relevance of the MINT frame redirection table. The below configuration can only be applied on the Evolution family devices. The device configuration allows to set the update interval for the MINT redirection table entries by choosing one of the three "mode" parameter values:
fixed: the redirection table is updated at intervals of 3 seconds. This mode is intended for static (fixed) links.
nomadic: the redirection table is updated at intervals of 1,5 seconds. This mode is intended for links connecting slowly moving objects.
mobile: the redirection table is updated at intervals of 1 second. This mode is intended for connecting mobile objects.
As shown above, a CPE with the MultiBS function activated, compares the current radio link performance with the maximum achieved. There is a possible scenario in which the radio link parameters deteriorate sharply due to the short-term influence of the interference and also recovers sharply afterwards. The CPE will break the connection with the BS in accordance with the MultiBS algorithm, despite the fact that the radio link deterioration had a short-term occurrence. The “mode” parameter selection affects the radio parameters' analysis when the MultiBS function is enabled, by setting the evaluation time interval. Thus, a device in a fixed mode evaluates the radio parameters over a three seconds interval and it is more resistant to link disconnection under short-term interference, than a device in a mobile mode, that evaluates the parameters more often.
Set the mobile mode on the Master and Slave devices:
As shown above, the MultiBS function speeds up the CPE roaming between the BSs, however, roaming is still accompanied by a short break in the connection. Link interruption avoidance can be achieved by using two CPEs on the moving object, combined with the functionalities of the AstraMUX. In this case, each CPE will independently establish a radio link with the BS and the AstraMUX will route the data traffic by choosing one of those links.
Let's look at the roaming algorithm with two CPEs (see Figure 8):
CPE1 and CPE2 have established links with the BS. In this case, no loop occurs because all radio devices are joined in one MINT area and the devices use a frame redirection table that takes into account the cost parameters.
The vehicle is moving, CPE2 breaks the link with BS1. CPE1 keeps the connection with BS1. The service hasn't been interrupted, because the data exchange between the vehicle and the control center is carried out via the CPE1-BS1 link.
CPE2 is looking for a BS to establish a radio link. CPE1 keeps the connection with BS1.
CPE2 establishes connection with BS2. CPE1 keeps the connection with BS1. When transmitting data, the AstraMUX uses one of the two links CPE1-BS1 or CPE2-BS2, with a lower metric.
The vehicle is moving, CPE1 breaks the link with BS1. CPE2 keeps the connection with BS2. The data transmission is performed via the CPE2-BS2 link and the service hasn't been interrupted.
To perform the configuration, PRF interfaces should be created on the CPE1 and CPE2 devices towards the AstraMUX. PRF interfaces should also be created on the AstraMUX towards the wireless devices. In addition, the switch groups configuration must be performed on the AstraMUX, not on the CPEs.
Keep in mind that any changes in the configuration from the command line, should be saved. The command to save configuration:
