What Other Factors Affect The Performance of an MMDS System?

Various components of an MMDS system affect performance or picture quality. Transmitters, channel combiners, transmission lines, antennas, path length, terrain, and downconverters all have key roles in the performance of an MMDS system.
Picture quality is the overall determining factor of the performance of an MMDS system. Picture quality is determined by comparing the picture image with the amount of perceptible "snow" or noise present. Carrier-to-noise ratio has an impact on the picture quality. All receive equipment has an inherent noise level (expressed as a noise figure in dB). Carrier-to-noise (C/N) is expressed by comparing the peak power of the video carriers to the power of the noise at the input of the receiver. MMDS system designed for a 49-50 dB C/N will provide excellent picture quality.

Internet access and telephony services

Operators are able to offer data and voice over IP services to thousands of users from each Base station chassis with minimal spectrum usage. Each chassis at the base station can support multiple cards for downstream and upstream transmission. In addition, six upstream channels can be supported on a single upstream card through Hex card. Such MMDS solution offers Quality of Service (QoS) capability, which allows operators to offer different tiers of services to different customers. The QoS feature is implemented on a per user basis. Different data rates can be committed to different users depending on the Service Level Agreement (SLA) signed with the operator. Both Committed Information Rate (CIR) as well as Maximum Information Rate (MIR) capabilities is offered. CIR is critical for voice applications and leased line applications. MIR allows operators to ensure that the system resources are fairly distributed to users in the network.
In summary, the key features of the MMDS BWA solution are:

-Point to Multipoint Broadband Wireless Internet Access for various markets. -Low cost solution. -IP centric solution set for SME, SoHo, Residential, and MDU segments. -Data, Voice, and Video services supported. -DOCSIS based system with enhancements for robustness and stability in challenging wireless environments -An HPNA base MDU solution readily available. -Proven DOCSIS MAC supports hundreds of users on a single channel. -Flexible bandwidth management and assignment with Quality of Service (QoS) support per user - Committed Information Rate (CIR), Maximum Information Rate (MIR) and Best Effort. -Ability to run multiple frequency bands from the same platform. -64 QAM Downstream Modulation enables high spectral efficiency while maintain link budget and optimal cell size. -16 QAM/QPSK downstream modulation enables multi-cell deployments. -Upgradeable, expandable and scalable. -DOCSIS based technology eases speed of deployment and installation.

The following System Diagram explains the architecture of the MMDS access system and its major components:

Solution consists of the Wireless Modem Termination System (WMTS), the Wireless Modem Unit (WMU) subscriber modem and a Network Management System (NMS). A typically deployed MMDS BWA system typically consists of multiple base stations, thousands of subscriber modems and a Network Management System. The WMTS is the Wireless Modem Termination System, which comprises of a chassis located at a base station site, connecting to multiple WMUs over the air to provide a "last mile" communication link between the service provider and the end user. The WMUs are located in subscriber premises and are connected to multiple computers and phone lines in each premise. The NMS manages the WMTS and the WMU network elements over the Internet using SNMP protocol. The NMS allows an operator to remotely monitor and control the WMTS and WMUs. The main management functions of the NMS are discovery, status polling, software download, configuration and monitoring.
The MMDS voice solution includes a VoIP PSTN Gateway at the Central Office which serves the purpose of converting IP packets coming from the Switch/Router (which receives/send packets from/to the WMTS) to voice calls that are forwarded to a Class 5 switch at the PSTN. The VoIP Gateway supports V5.2 connectivity to the PSTN. The Gateway has an integrated Call Agent (Gatekeeper) that call set up within in the system. The architecture offers transparency to important voice call features from the Class 5 switch. At the CPE end, an external Media Terminal Adaptor (MTA) device is connected to the WMU using the 10 BaseT interface. The MTA has multiple RJ11 ports to supports multiple POTS phones or Fax machines within a premise. It also has a 10 BaseT interface, which can be connected to a router/hub to connect several computers within a premise. The maximum number of MAC addresses that can be supported on each WMU is 75. The solution offers QoS capability and voice users on the network are supported with Committed Information Rate (CIR) capability. Industry standard voice codecs including G.711 and G.729A are supported by the system.
A key differentiator of such solution is the incorporation of a DOCSIS based standard. DOCSIS is commonly associated with the cable industry, to provide medium access control (MAC) for sharing of the frequency channel amongst hundreds or even thousands of simultaneous users. Since DOCSIS was primarily developed for the cable industry, were introduced a number of wireless enhancements to enable robust operations of the modems over the air. These enhancements include: o 64 QAM, 16 QAM and QPSK downstream modulation.
- +/-100 kHz frequency compensation at CPE for offset, drift over temperature and aging enabling the use of lower cost CPE transceivers.
- Wider dynamic range.
- More robust power control optimized for wireless applications.
- Spurious emissions and harmonics are suppressed by 60 dBc (when combined with an appropriate transverter). These enhancements allow the V3000 to meet the requirements of the FCC and to provide robust performance in the RF path.
- Equalization to address ISI due to multipath.
- Option for upstream antenna spacial diversity to increase coverage.
Capacity Planning
- The capacity of the MMDS system (downstream and upstream) depends on several parameters including the frequency re-use scheme selected. Some of these parameters include:
- Channel BW
- Modulation Type The following table includes a very popular MMDS configuration, 2 downstream sector, 4 upstream sector, and provides a summary of data rates throughput figure for the Base Station and for the sector:

This configuration allows the operator to supply 25 Mbps to each of two 180° sectors and 12Mbps to each of four 90°upstream sectors all supported by the following equipment at the Base Station:
- 1 x WMTS
- 2 x Downstream cards within the WMTS
- 4 x Upstream cards within the WMTS
- 2 x Downstream (Upconverter) Transmitters
- 2 x 180° Downstream antennas
- 4 x 90° Upstream Antennas
- 24 x Upstream (Downconverter) Receiver (combiners can be used to reduce the number of receivers required)
The use of a 1.6MHz channel in QPSK mode is quite common at MMDS because it is more robust in MMDS environments.

Summary

MMDS BWA Solution is the best solution on the market available today. Some of the key differentiators of the MMDS solution are:
A DOCSIS based platform leads to lower cost modem platform than the competition. Modems are based on DOCSIS based platforms, thus the price of the modem product is lower than the competition and will continue to be cost reduced based on the availability of newer, more integrated DOCSIS based components.
A DOCSIS based platform features a more robust MAC than the competition. The DOCSIS based MAC is highly sophisticated and can handle hundreds or even thousands of modems simultaneously on a single channel. This MAC has already been proven out in the cable industry as a robust TDMA platform that can scale to support hundreds of users.
DOCSIS based leads to seamless integration of the many third party software applications developed for DOCSIS based products, including service provisioning systems, third party billing systems, robust DHCP/TFTP server systems, etc.. This means that customers can take advantage of this 3rd party development.