Motorola High Performance Data Overview |
Motorola are being dickheads (as usual) on releasing decent technical info on their new police/fire MDT system, this is what we've found so far...
Motorola High Performance Data
Proposed Solution - Technology Overview
To meet the need for a wide-area wireless data solution, Motorola has proposed the High Performance Data (HPD) technology. The HPD technology offers high bit rates in standard 25 kHz channels within the 700 and 800 MHz bands. To meet the requirements for mission critical data service, HPD offers significant advantages in the key areas of coverage, throughput, and standards.
The HPD Coverage Advantage
Motorola has designed HPD to offer coverage that is approximately equivalent to typical voice coverage. Although this is a very aggressive coverage goal when considering the much faster bit rates that HDP is capable of (96,000 bits per second), Motorola recognizes the value of maximizing coverage to keep site costs as low as possible. For example, if an increase in data speed results in loosing half of the range from a given site, then the coverage area is theoretically reduced by 75% and the system would require four times as many base sites to provide coverage that would be equivalent to that of the lower bit rate.
With all things considered equal, physics dictates that for a given channel bandwidth the coverage decreases as the bit rate increases. If the transmit power of base stations and mobiles could be increased, the lost coverage could potentially be recovered; however, the FCC limits transmit power to control noise and interference within any given band. Therefore, power cannot be increased indefinitely to address the issue and other methods of maintaining coverage are required.
To maximize potential coverage, HPD technology implements several key features:
Advanced Modulation Techniques
There is a fundamental tradeoff in communication systems with the use of simple verses more complex transmitters and receivers. Simple hardware can be used in transmitters and receivers to communicate information. However, to increase the bit rate while continuing to use the simpler hardware, more spectrum is required to maintain the same level of coverage performance. Since the spectrum is limited by the bandwidth of the channel, the only option is to suffer coverage degradation. Alternatively, more complex transmitters and receivers can be used to transmit higher bit rates while remaining within the channel's bandwidth limitation. This transition to more and more spectrally efficient transmission techniques requires more complex hardware and is the market trend considering the limited spectrum available today.
In the past, traditional wireless data networks used Frequency Shift Keying (FSK) modulation, which requires simple hardware and is very easy to implement. As an example, Motorola's RD-LAP protocol used a 4-level FSK modulation to achieve a bit rate of 19.2 kbps in a 25 kHz channel. To achieve higher rates than 19.2 kbps, higher order FSK modulations are required such as 8-FSK, or 16-FSK.
The problem with FSK is that the modulation decreases significantly in bandwidth efficiency as the modulation order is increased. With this in mind, HPD was designed using a multilevel Quadrature Amplitude Modulation (QAM) method that achieves a high bit rate using limited bandwidth available. HPD incorporates the use of three QAM formats and automatically adapts between these 3 modulation levels which are QPSK (4-QAM), 16-QAM, and 64-QAM.
Further worth noting, both QAM and QPSK modulation techniques are used by IEEE 802.11 (WiFi), IEEE 802.16 (WiMAX) and 3G (WCDMA/HSDPA) wireless technologies. The use of adaptive modulation allows wireless technologies to optimize throughput, yielding higher throughputs while also covering long distances. The HPD technology is designed to also achieve these critical goals.
Adaptive Modulation
The use of adaptive modulation allows a wireless system to choose the highest order modulation depending on the channel conditions. As the range increases or the channel conditions become more challenging, the modulation automatically adapts down to lower order modulations, such as 16-QAM or QPSK, to maintain coverage. However, in good signal conditions the higher order modulations, 64-QAM or 16-QAM, are used for increased throughput. With the use of adaptive modulation, the system is enabled to better overcome the loss of coverage that is experience with fixed modulation rate systems.
HPD offers bit rates up to 96,000 bits per second (bps). At such a high rate, coverage will be reduced as physical law dictates; however, HPD has the ability to automatically adapt to lower rates of 64,000 bps (16-QAM) and 32,000 bps (QPSK) as required to insure that coverage is extended into weaker signal areas.
Advanced Forward Error Correction
Channel coding is the best method for transmitting information with fewer errors in weak signal environments. Stronger Forward Error Correction (FEC) coding has the ability to extend coverage beyond the ability of a weaker code. In the past, common codes such as Reed-Solomon, Trellis, and Viterbi have been used as methods for achieving FEC. In 1993, a major advancement in coding, internationally known as Turbo coding, was introduced. Turbo coding enables data communications to come very close to the theoretical limits of a channel, offering significant benefit in coverage performance.
HPD incorporates Turbo coding as a state-of-the-art method for achieving forward error correction. In weaker signal areas where receive errors tend to be the highest, this strong FEC method offers the potential of correcting errors that would otherwise have been uncorrectable with weaker algorithms. Thus, the HPD method enables potential coverage in areas that would have failed due to excessive errors.
Diversity Receive Capability
The standard HPD configuration supports two receive paths on each base station to mitigate fading effects that are common to RF environments. With this approach, two receive antennas are used to capture signals from two spatially different locations on the same tower at a given base site. If one antenna experiences a deep fade but the other captures signal with reasonable quality, the received signal can still be successfully decoded. This method has been proven to provide significant coverage benefits in non-line-of-sight coverage areas.
Efficient Retry Method
It is a known fact that larger messages have a lower probability of being successfully received in comparison to shorter messages. When a message transmission fails in many systems, the entire message is retransmitted and there is no reduction in message size. HPD offers a retry method that retransmits only the portions of a message that have errors rather than retransmitting the entire message. Using this approach, the retried message will be smaller. This approach offers a higher probability of a message being received and ultimately results in improved coverage and throughput.
This method, known as Selective Automatic Repeat Request (SARQ), has been implemented in HPD and is also the method approved by APCO in the P25 wireless data standard.
High-Speed Vehicle Support
In mission critical systems, the ability to support data communications with vehicles moving at high rates of speed is mandatory. With this requirement in mind, HPD was designed to maintain data integrity and reliability at vehicle speeds up to 120 miles per hour.
Non-Line-of-Sight Operation
The HPD offering incorporates the use of a land mobile radio variant of Orthogonal Frequency Division Multiplexing (OFDM) as a critical performance enhancing technology. As the symbol rate for a given channel bandwidth increases, the performance degradation due to multipath delay spread also increases. In the mobile environment, the transmitted signals take many different paths before arriving at a receiver. These paths include reflections off of buildings, cars, mountains, and many other objects. This is referred to as multi-path. Because multiple reflections of the transmitted signal arrive at the receiver at different times, this results in intersymbol interference (or signals "walking on top of each other") which the receiver many times cannot sort out. As the symbol rate increases, multipath interference becomes a greater concern and results in significant coverage loss if not effectively mitigated. OFDM is a well-known technique for combating multipath that has only recently become practical for commercial applications.
OFDM has recently provided significant performance improvements in the wireless LAN market for the 802.11a standard as opposed to the single-carrier direct sequence CDMA physical layer of 802.11b. OFDM can provide the same benefits to wide-area land mobile radio networks as it does for the local-area networks. The basic idea of OFDM is to divide the available channel (25 kHz in this case of HPD) into many subchannels. Rather than transmit data using a single frequency carrier, each sub-channel has a sub-carrier that transmits a significantly lower symbol rate signal. In essence, the transmitted signal is a collection of many lower rate signals that when combined together in the receiver result in a high data rate. Using this OFDM method, the multipath effect is mitigated through the transmission of the slower symbol rates on the sub-carriers.
In short, OFDM is a robust and efficient method for providing non-line-of-sight wireless access in the HPD system. The straightforward way it combats multipath, the high spectral efficiency it provides, and the multiple access efficiency it enables are well suited for providing higher data rates to multiple users without significant coverage penalties.
Improved Receive Sensitivity
In the digital modulation world, detection is the process by which a receiver attempts to determine what information was actually transmitted. For FSK modulation, a simple non-coherent receiver is typically used because the detection process makes decisions based on one dimension, which are shifts in frequency. For QAM modulation, a more complex coherent receiver is used in the detection process to make decisions based on two dimensions, amplitude and phase. Adding another dimension to the process further improves the sensitivity of the receiver which results in increased coverage performance.
Along with the use of QAM modulation, HPD uses coherent modulation methods that bring this added coverage advantage.
Efficient Frequency Reuse
HPD is designed to allow the reuse of frequencies to cover large geographic areas. HPD can be deployed in a cellular-like fashion using as few as 7 channels in a repeating pattern. This gives HPD the flexibility to be deployed over small city areas, large counties, or even state-wide regions using only 7 channels to achieve the required coverage.
Transmitted Power Control
HPD has implemented a method for automatic adjustment of transmit power by mobile units. This enables the mobile units to achieve the required quality of transmitted signal using the minimum required radiated power. Transmitter power control helps to minimize interference levels within the channel, thereby enabling coverage benefits through interference reduction.
For the coverage advantage, HPD implements several technological advancements that position HPD as a highly reliable wide-area wireless technology that offers coverage equivalent to Project 25 voice and data coverage, however, at significantly higher bit rates.
The HPD Throughput Advantage
Motorola's objective is to satisfy two conflicting goals, which are maximizing coverage and maximizing throughput. The actual realized throughput and capacity limits in any given system will be a factor of several variables. Such variables include site density, load distribution across system resources, service area reliability, antenna system design, application profiles, full/half-duplex device operation, and more. Because there are so many variables that define the throughput and ultimate capacity of a system, Motorola would be amiss to state such levels without a complete system design in place. However, Motorola has invested significant resources in developing the HPD technology to insure that greater throughput levels are achieved in any design scenario.
To maximize throughput, some of the key features offered by HPD include:
Fastest Over-the-Air Rate
HPD offers a maximum bit rate of 96,000 bits per second, the fastest rate commercially available in 25 kHz channel bandwidths and a rate that only Motorola has achieve to date. Even at the lower rates of 64,000 and 32,000 bits per second, HPD offers significant speed advantages over many competitive offerings. Motorola anticipates the average channel bit rate to exceed 64,000 bits per second in most implementations.
Adaptive Coding
Although FEC coding is necessary to achieve coverage goals, FEC comes at a price in the form of overhead bits in each data transmission. To minimize the impact of this overhead, HPD includes a methodology for controlling the amount of overhead used for forward error correction. For the strongest error correcting capability in weaker signal areas or for critical portions of the data stream, HPD automatically varies FEC coding rates between 1/2 and 2/3 as required by current channel conditions. With less FEC overhead, user data throughput is increased; however, if more FEC strength is required to deliver a message, HPD is able to make the adjustment to prevent further retries of a message, which also conserves channel capacity.
Advanced Multi-Access
HPD provides an extremely efficient method for supporting multiple users on a single channel. The HPD approach uses a reservation method to prevent users from transmitting messages simultaneously which result in failed transmissions and, ultimately, wasted channel capacity.
The HPD method implements a reservation based method using slotted-Aloha for controlling access to the inbound channel. Using this method, the transmission of data, acknowledgements, and even retries occur in reserved time slots so that there is no threat of collision. Small time slots are provided for requesting access to the channel, or in other words, making the reservation. These smaller time slots are the only time that contention (or collisions of messages) can occur. Overall, channel access efficiency is greatly improved which increases the potential data throughput on a channel.
Efficient Retry Method
HPD's approach to retries also enhances throughput capability. If retried messages are smaller and contain only the portions of the original message that fail, then the channel resources are not burdened with repeat data that has been successfully received. In this regard, more of the channel is freed up to support other data and ultimately the channel capacity is improved. In many systems, retransmissions include the entire message and there is no capacity benefit.
From a user perspective, response times are often longer when operating in weaker signal areas where retries are common. The time between retransmissions of messages often varies from 2 to 4 or more seconds in many deployed wireless systems. With HPD, the average time between retries is on the order of 500 milliseconds, resulting in faster response times even in fringe areas of coverage.
Data Optimized
HPD has been optimized as a narrowband packet switched data service. In most systems supporting voice and data services over the same channel space, voice conversations are typically given priority while data transmissions are queued for future delivery. As voice traffic increases in these systems, data throughput decreases and can be severely limited during peak hours of operation. HPD is dedicated to data service and unaffected by voice traffic so that mission critical data transmissions are prioritized at all times and data throughput potential is not compromised.
Full-Duplex Device Operation
HPD supports full-duplex device operation which enables the transmission and reception of data simultaneously. With full-duplex capability, the modem is able to send multiple data messages while waiting for acknowledgements. In a half-duplex device, the device is transmitting, receiving, or switching between transmit and receive. As such, the throughput to a half-duplex device is less than that available to a full-duplex unit.
With the full-duplex capability built into HPD modems and the way HPD automatically schedules inbound ACKs and retries, support for common industry standard protocols such as TCP and HTTP is feasible.
Sliding Window
HPD implements a sliding window protocol that permits a greater amount of channel throughput (70-80%) to be consumed by a single subscriber radio. The result is much greater throughput rates are available to individual users compared to a stop-n-wait protocol, which typically prohibits more than 30% of the channel throughput for a single user. With HPD, channel throughput is not wasted when it is available. However, the channel bandwidth reservation feature ensures that no single user can dominate channel resources when multiple users need to send data simultaneously.
For the throughput advantage, HPD implements several technological advancements that position HPD as an efficient, high-throughput, packet data service for 25 kHz channels in the 700 MHz and 800 MHz bands.
The HPD Standards Advantage
Motorola understands the value of adhering to standards to protect financial investments, achieve interoperability, and to conform to other existing standards in common use. Motorola developed HPD with full consideration of standards and incorporated these key features:
Migratable
TIA902 is the standard defined by public safety users and industry leaders for wideband data in the 700 MHz band. As defined, TIA902 supports channel bandwidths of 50 kHz, 100 kHz, and 150 kHz. In support of this standard, 700 MHz and 800 MHz HPD modems can be software upgraded to the 50 kHz TIA 902 standard. The RF modems represent a large investment in a typical system deployment; thus, this migration path to the 700 MHz standard protects the initial investment.
Scalable
With the software migration from HPD to the TIA902 standard, the modem scales to a much higher performance level. While many HPD features are also contained in the TIA902 standard, there is a significant increase in available data rate. In a 50 kHz channel, TIA902 provides a maximum burst rate of 230,400 bits per second. In the transition from HPD to TIA902, the maximum RF efficiency increases from 3.8 bits per second per hertz to 4.6 bits per second per hertz. With all elements considered the potential throughput more than doubles.
Industry Standard IP Addressing
HPD supports industry standard IP addressing. With IP addressing, there are no proprietary interfaces to be implemented, saving development time and costs. Also, there is no middleware required for the purpose of IP tunneling or "IP enabling" the network.
On the network side of the system, network hosts interface to the HPD system in the same manner as a common network router to send IP datagram's to mobile units. On the mobile client side, the client computer interfaces the HPD modem using the industry standard Point-to-Point Protocol (PPP). The modem interface also utilizes 10BaseT Ethernet as opposed to the slower serial interface commonly used in narrowband networks.
TCP Compatible
Along with the Internet Protocol (IP), the Transmission Control Protocol (TCP) continues to be the best known and most widely deployed protocol used to communicate across interconnected LAN and WAN systems to support both custom and common applications such as electronic mail, terminal emulation, file transfer, and web browsing.
To meet this challenge, several key HPD design features make TCP support feasible. Key features include the ability to send multiple messages while waiting for ACKs (windowing), automatically scheduled ACKs and retries, reduced time between retries, and full-duplex modems.
Depending on the details of the system design, including all of the design variables, a single HPD channel will provide excellent data throughput. With the advancements, efficiencies, enhancements, and standards built into the HPD technology, Motorola is positioning HPD has a standards-based, high-coverage, high-capacity wide area solution for 25 kHz channels.
Customer Network Interface
The Customer Network Interface (CNI) is the network that connects the HPD network and the Customer Enterprise Network (CEN), where the data application servers will reside.
Since the CEN is administered independently from the radio network, Motorola must coordinate the IP address space to be allocated for the different networks. Motorola will provide the IP addresses belonging to the HPD network and will recommend IP addresses to be used for the CEN.
Border routers are used to connect to the CEN to the HPD network. One side of the border router provides an interface with the CEN while the other side of the border router attaches to a peripheral network to interface with the Gateway GPRS Support Node (GGSN) router on the edge of the radio network.
The intermediate network segment connecting the HPD system to the CEN is referred to as a Demilitarized Zone (DMZ). The DMZ functions to provide a separation of addresses in each network, and creates a safe meeting place between the two networks. The addresses inside the DMZ subnet are used only for linking the networks, and are not advertised outside the DMZ boundary. A server or client knows an address to enter the DMZ, but is not exposed to either DMZ subnet addresses or addresses in the target network. The Network Address Translation (NAT) functions (at each network's router) hide the internal addresses of each network from the other. Address assignment and coordination within both the CEN and the DMZ subnets are customer defined; however, due to security and performance considerations Motorola will assign addresses belonging to the HPD system network.
Gateway GPRS Service Node
The Gateway GPRS Support Node (GGSN) is a special purpose router that provides various services in support of HPD data operation. Among those are separation of IP address spaces between the HPD radio system network and external customer networks, DHCP address management, and tunneling of radio system datagrams into and out of customer networks.
The device is used in the HPD system to provide connectivity between the HPD radio system network and other enterprise networks. It is used to "tunnel" datagrams from the enterprise network to the Packet Data Gateway (PDG), which ultimately passes the datagram on to a specified subscriber unit operating on the "closed" Motorola radio network. A GGSN does the following:
Packet Data Gateway
The Packet Data Gateway (PDG) is made up of two separate functional elements - a Radio Network Gateway (RNG) and a Packet Data Router (PDR). The PDG interfaces between the GGSN and the Motorola radio network.
Packet Data Router
The PDR interfaces with the GGSN and controls the routing of data messages between the serving RNG and the GGSN. Additionally, the PDR maintains a database of data-capable Subscriber Units (SU).
The PDR provides a packet data "home" for all SUs that have been Home Zone mapped to that zone for data operation. It sends packets to, and receives packets from the RNG. It also operates with the GGSN to terminate the HPD system's IP address space and provide address translation between the HPD system's IP network and external "customer" networks.
The PDR is responsible for managing data context activation and deactivation. That is, the PDR manages the process of establishing data services and connections for all active SUs. It authorizes and approves context activations by validating provisioning from the network management subsystem against the specified request from the SU. The PDR also determines when context deactivation for a SU is needed. Context deactivation may occur for the following reasons:
Radio Network Gateway
The RNG is the second of two components within the Packet Data Gateway (PDG). This component interfaces between the Packet Data Router (PDR) and the Subscribers in its own zone.
The RNG in a zone provides a link layer termination point for all the sites in that same zone. The sites and the RNG route data packets over the infrastructure links between remote and master sites in the zone. The RNG receives packets from, and sends packets to, any of the PDRs in the system (that is, PDRs in the same or even other zones). The RNG also holds records of all subscriber units currently affiliated with sites in its zone, acting as the Visitor Location Register (VLR) for data.
The RNG maintains a database of context activated SUs registered in its zone, which is based on actual SU location. SU mobility is tracked on a site-by-site basis. Location information is updated via a mobility "push" from the Zone Controller (ZC). Additionally, the RNG queries the ZC's VLR to verify SU location.
The RNG is responsible for processing and routing data messages. Processing entails breaking down the data message and formatting it into message blocks (CAl format) compatible for over-the-air transfer. The RNG then routes to the appropriate destination device (outbound to the site controller and inbound to the PDR). The RNG performs error checking of all inbound messages that SUs have formatted for over-the-air transfer. After processing, the RNG forwards the message to the PDR.
Zone Controller
For data activity, the Zone Controller (ZC) is responsible for managing mobility information. This is the same zone controller that is also used to support voice operations.
The ZC provides mobility information in the form of "mobility pushes" to the PDR component of the PDG. The PDR uses this information to keep the data system in sync with current SU mobility status. Information that the ZC provides indicates an SU's activity with respect to registration, deregistration, site roaming, and zone roaming. Note that mobility "pushes" occur on every ZC mobility update.
Network Management
The Network Management (NM) suite previously defined to support voice operations is the same NM suite used for the HPD portion of the system. Thus, the entire voice and data solution is managed from the same set of NM applications. The suite includes the ability to perform diagnostics, provision subscriber units, monitor system components, obtain statistical information, configure and control network elements, and monitor system faults.
Mobile Subscriber Unit
Motorola has proposed the HPD 1000 radio modem as the mobile subscriber unit for wireless data services. The HPD 1000 combines the radio and modem function into a single device.
The HPD 1000 supports the mobile computing device through an industry standard PPP connection, which the application will use to exchange IP datagrams with the application server within the customer enterprise network. The PPP connection is physically supported via USB 2.0 connection. Alternatively, an Ethernet connection is available on the HPD 1000 to support a PPP over Ethernet (PPPoE) connection.
To initiate service on the HPD network, the mobile registers for packet data service through a process know as context activation. This process is always triggered from the subscriber-end of the system when the user begins a data session.
The HPD 1000 is a full-duplex device that includes the full HPD feature set, including adaptive modulation, forward error correction, interleaving, selective ARQ, adaptive FEC code rates, reservation-based slotted-Aloha contention control, a land mobile variant of OFDM, and more.
Programming Software: ASTRO 25 Mobile CPS R12.00.00 & TUNER R05.04.00
(or higher - new versions can't read older FLASHports)
Programming Cable: HKN6180 (RS232), HKN6177A, HKN6178A (USB)

