[Broadband Wireless: In Transition (Wireless Review 4/15/99)]
Article from Wireless Review dated 15 April 1999
Source:
wirelessreview.com
(Although this article is a bit old, I think its still relevant.)
Broadband Wireless: In Transition
As point-to-multipoint technology emerges, what happens to point-to-point?
By Jarlath Lally
Broadband wireless and point-to-multipoint technology are attracting a lot of
attention. Point-to-multipoint technology is the wireless vehicle that is
potentially capable of addressing almost all technological/business
requirements. Technology efforts target three market segments: small-, medium-
and large-size businesses, SOHO and eventually residences. Point-to-multipoint
solutions intend to satisfy common end-user needs and system requirements that
prevail in all three markets. (See Table 1)
End-User Needs
• High-speed access
• Low perceived delay
• Quality of service
• Value
• Minimal, compact, unobtrusive equipment
System Requirements
• High-quality communications to any customer terminal supporting mixed services
• Direct and seamless integration with existing infrastructure
• Rapid and low-cost hub and CPE installation
• High system availability (99.999%)
• End-to-end network management
• Scaleability
Table 1. Common end-user needs and system requirements
Unfortunately, a lack of standards as well as nebulous operator requirements
and market aspirations have slowed point-to-multipoint progress. In the long
term, point-to-multipoint will prevail. Today, point-to-point systems can meet
your needs in more ways than one.
The System
As solutions emerge and product philosophies solidify, broadband wireless
systems are exhibiting many common characteristics. The typical model uses
hardware that allows you to integrate any existing networking/communications
technology seamlessly with microwave, millimeter-wave technology. The radio is
independent of the baseband (networking/communications) elements and ultimately
transparent to the end user. In these systems, point-to-point radio links are
used for backhaul, with point-to-multipoint radios used for delivering services
to customers. But in the short term, point-to-point radios can serve both of
these functions.
Most systems comprise three major elements: customer premise equipment (CPE),
the hub (sub-divided into sectors) and the head-end, with end-to-end network
management. You can use fiber or point-to-point OC-3 microwave radios for
backhaul requirements.
The CPE is made up of a network interface unit (NIU) — a black box capable of
interfacing with existing customer network devices — and a radio terminal with
a directional antenna aligned with the sector antenna at the hub site. The
NIU’s key role is to interface between the point-to-multipoint radio network
and the end user’s existing communications infrastructure. Systems must be
scaleable and interoperable to accommodate various dynamics as well as growth.
At the hub, traffic is distributed to and from each sector. The number of
customers that it can support depends on hub capacity, bandwidth usage and
guaranteed availability. Availability has a bearing on overall economics
because it affects cell radius and consequently the number of customers it can
serve as well as inter-hub spacing. (For the same hub output power, higher
availability implies smaller cells.)
The hub interfaces to the backhaul transmission network via a SONET OC-3
interface. The system will require additional sectors to sustain
quality-of-service guarantees.
The time division multiplexing/TDMA combination has emerged as the preferred
access solution. It allows optimized spectrum use allocated to each subscriber
for either dedicated bandwidth or bandwidth-on-demand applications. ATM has
become the preferred solution for bandwidth management. Its overall flexibility
for multimedia service integration, albeit with overhead penalty, allows
flexible bandwidth partitioning between services, coupled with grooming and
cross-connect capabilities.
The complex system demands comprehensive network-management facilities to
optimize bandwidth deployment based on service offerings and to allow graceful
network expansion. The SONET/ATM combination that inherently supports TMN
functionality and mechanisms for end-to-end network management satisfies this
requirement.
The actual topology of a point-to-multipoint network is simple. Existing fiber
infrastructure is used where possible, but you can augment it by using
point-to-point OC-3 radios to maximize hub-deployment options and minimize
deployment time. In some cases, there are cost issues and geographic
impediments that prohibit fiber from supporting hub location. So, from the
outset of network deployment, the OC-3 point-to-point radios will be a key
element in system integration.
An Immediate Solution
If you have purchased substantial spectrum, you are under pressure to start
generating revenue. The point-to-multipoint products available today are
proprietary with no standards to validate against, and the results of trial
deployments are still somewhat inconclusive. But point-to-point SONET access
radios (OC-3) and PDH radios are available.
Initial target customers will be mid- to high-end users. Carriers will sign up
high bandwidth and maximize revenues through dedicated customer access during
the first phases of network deployment. Rather than waiting for viable
point-to-multipoint platforms, point-to-point radio links can serve this market
today. Bandwidths delivered to the subscriber will vary from multiple DS1s
(T1s) or DS-3 at the PDH level to 155Mb/s OC-3 at the SONET level. The term
multiple point-to-point describes the network configuration where
point-to-point radio links share a common hub.
The multiple point-to-point network uses existing in-building wired
infrastructure to support service deployment. SONET add/drop multiplexers and
off-the-shelf NIUs or wide area network access switches/concentrators provide
seamless connectivity to the in-building infrastructure (PBX, router).
Ultimately, one piece of equipment will serve both functions. Using low-cost
PDH point-to-point radio systems can mitigate deployment cost concerns, and
they are similar to point-to-multipoint estimates for the same service levels.
In fact, in most current point-to-multipoint network variations, point-to-point
radio costs compare with the average user bandwidth requirements that exceed
two T1s.
At the outset, your key network design consideration should be to ensure that
point-to-multipoint is the long-term goal. But point-to-point systems don’t
have to become redundant. If the network is designed carefully, the existing
point-to-point infrastructure can complement the point-to-multipoint system.
Ultimately, the point-to-point network will become a launch platform for the
point-to-multipoint system supporting the backhaul requirements for each hub
(155Mb/s – OC-3).
RF Considerations
In the transition to point-to-multipoint networks, carriers need to address RF
planning issues. Fixed radio access requires a more rigorous approach than
mobile planning. You have to consider basic requirements, including line of
sight for all key commercial and industrial areas, point-to-point link path
planning and hub location. Optimal hub spacing will depend on link margin,
propagation characteristics and availability design goals. In the past, when
large spectrum blocks have been allocated, there has not been an emphasis on
using spectrally efficient radios. As a result, some networks such as the 23GHz
in the United Kingdom have experienced frequency congestion earlier than
expected. Equipment spectrum efficiency is a key factor when partitioning your
frequency allocation between point-to-point and point-to-multipoint systems.
For example, by using spectrally efficient point-to-point OC-3 or PDH radios,
you maximize and reserve the amount of point-to-multipoint revenue-generating
spectrum for long-term use.
Specifications
As the network evolves, point-to-multipoint standardization will enhance market
confidence and reduce development expenditures. With anticipated competition
from other technologies such as satellite for broadband service deployment, the
price of subscriber equipment has to reach commodity levels.
The Broadband Radio Access Networks (BRAN) project, which ETSI established to
produce unified standards for broadband fixed wireless applications, is
spearheading these specifications. Most notably, it has developed a common
reference model with the ATM Forum. This model specifies radio subsystem
development that matches the wireless extensions to the Forum’s ATM
specifications.
Domestically, the IEEE’s 802.11 wireless LAN and newly formed IEEE 802.N-West:
Broadband Wireless-Access group met with BRAN representatives and Japan’s
Multimedia Mobile Access Communications council to encourage cooperative
development of global standards for all broadband wireless systems.
The Ultimate Challenge
Ultimately, the challenge for broadband wireless licensees is to design, build
and operate high-capacity, point-to-point and multiple point-to-point networks
that can evolve to support point-to-multipoint easily, achieving wireline
quality of service. If wireless is going to compete with fiber effectively, it
must match the correct level of service to the right application. |
