Broadband Access Networks
Systems
Our efforts in this area center around solving the
broadband subscriber access problems, e.g., those associated with hybrid fiber /
twisted-pair, hybrid fiber / coax and hybrid fiber / wireless networks
evolution. These networks are planned to be transparent on the optical side, so
far as advancements on the backbone network are concerned. For example,
migration toward IP / MPLS over Dense-Wavelength Division Multiplexing (D-WDM)
makes the optical SONET layer appear unnecessary.
Local access technologies (fiber, coax, ISM, UNII bands and mm-wave bands) are
becoming widely available at affordable costs to all potential service providers:
LECs, cable-television operators, alternate-access
providers, electric utilities, and wireless-communications companies. All
access products are relatively similar in cost, and offer comparable operations
savings. Important differentiators are service and product reliability, service
that some may offer (e.g., wireless connectivity). Our research activities
focus on all these factors as they relate to hybrid fiber / coax (HFC), HFC
overlaid with FTTC, FTTC (or HFC) integrated with
Return to CICTR Research Areas
Wi-MAX Access Systems
IEEE 802.16e, the standard for Mobile WiMAX, is expected to be published by the end of 2005 and
the Mobile WiMAX will be launching its service in
Since IEEE 802.16e, the mobile version of
IEEE 802.16-2004, will be published soon, the focus of 802.16 is expected to be
changed from fixed subscribers to mobile subscribers with various form factors;
Unlike the wired networks, wireless
networks are highly dependent on communications channels; radio channels are
dynamic, correlated, unreliable and very expensive. This is why the performance
will be highly dependent on how well the radio resource management supports QoS requirements even if QoS
might be luxurious in early stages of the Mobile WiMAX
market. Therefore, several cross layer issues in
In multi-user environments, especially in
wireless fading channels, multi-user diversity in radio resource management is
one of key elements in maximizing the throughput. Multi-user diversity is a
form of selection diversity. Since different users experience independent
time-varying fading channels in wireless networks, resources shall be allocated
to the user that has the best channel quality in order to maximize the system
throughput. Multi-user diversity drew attention since tracking the channel
fluctuations of the users is getting more accurate and faster. Hence, the
diversity gain increases when dynamic range of the fluctuation increases but,
the gain is limited in environments with slow fading. In slow fading,
multi-user diversity hardly satisfies all QoS
parameters at the same time, especially the fairness among all different users.
Ultimately, radio resource management need to implement a combined form of
multi-user diversity and fairness scheduler.
The architecture requires
development of critical components for the transceiver and systems. This
includes providing cost-effective distribution and coverage to subscribers,
utilization of low-cost monolithic IC and antenna technology, and implementing
effective transceiver linearity, modulation and coding and
Related issues are being
investigated:
·
BECHTEL Telecommunications Journal:
§
Jungnam Yun, M. Kavehrad,
“PHY/MAC
Cross-Layer Issues in Mobile WiMax,”
Bechtel Telecomm Technical Journal, Vol. 4, No. 1, January 2006.
- Opportunistic Communications –
Adaptive-Rate Techniques, Dynamic Network Resource Management
- Multi-Input-Multi-Output (MIMO) Systems; (see,
e.g., Broadband Wireless Local Area Networks )
- Cellular Network Systems; Dynamic TDD:
·
Penn-State
Research News:
New
Allocation Technique Boosts Efficiency for Wireless Internet Access
·
The
·
ASME:
Clarifying
Wireless High-Speed Internet
·
Innovation
Reports: Allocation
technique boosts efficiency, minimizes interference for wireless internet
broadband
- Quality-of-Service (QoS)
Metrics
- RF Propagation Modeling and Channel
Characterizations.
Broadband Transmission over Power
Lines
A Solution to the Global Digital Divide Problem:
The medium-voltage (MV) power
grid, typically carrying Megawatts of power at 11,000 V, reaches within a few
hundred meters of most inhabited places on earth. The same grid is an excellent
communications medium, offering bandwidths well beyond 100MHz and potentially
more, with
The power distribution grid resembles an omnipresent, widely
branched hierarchical structure. The structure of the medium (MV) and
low-voltage (
Many service providers are interested in introducing the next
generation broadband access to residential homes and small home offices (SOHOs) via power-line distribution network architecture,
termed Broadband over Power-Line (BoPL) transmission
network, in the not too distant future. A typical scenario for such an access
network is shown in Figure-1. In search of a proper end-to-end feasibility test
of the anticipated physical-layer design, we are conducting investigations on a
system level model. The work presents conceptual designs, analyses, computer
simulations and some experiments on a BoPL
transmission configuration to assess the potential interference problems.
Fig.-1 Power-Line
Broadband Access Network Architecture
Despite the enormous potential, there is some
skepticism about the technology and its commercial viability. This is due to
several technical problems and regulatory issues that as yet remain to be
resolved. Some of these issues are
listed below:
·
Power line channel is harsh due to discontinuities (impedance
mismatch), ground effects, interference and noise, thus difficult to model.
·
Regulatory issues naturally arise due to unshielded nature of
overhead power lines, which are both the source and target of electromagnetic
interference.
·
Since communication over power networks is basically wire-borne,
suitable measures have to be developed to prevent inadmissibly high signal
radiations, i.e., interference to and from other services needs to be remedied.
In a relatively complex grid of nodes and lines, discontinuities
caused by Impedance Mismatch between a node (e.g. a transformer) and a wire
line connected to the node, create reflections. These reflections give rise to
a frequency selective multi-path. There is also possibility of resonance effect,
due to standing wave formation, on transfer (magnitude and phase versus
frequency) responses of an end-to-end line between points A and B on the
overhead MV power line grid, as shown in example below [1]:
Transfer function
between grid nodes A and B of the network in Fig.-5 of
[1] with discontinuity at nodes Impulse
response for the path between A and B in Fig.-5 Of [1]
The impairments of Power-line Systems are
similar to those of
We need to remember that overhead MV power-lines are exposed. The
use of electric power network to carry RF waves is not unconstrained, because
by occupying a frequency band of about 500 KHz to nearly 100 MHz, a frequency
overlap is created with some existing practices such as; the entire HF band
services, long, medium, and short-wave radios and amateur radio bands, as
air-borne power lines also act as antennas, transmitting and receiving
interference to and from the surrounding environments.
On April 27, 2004 NTIA released a Phase-I study that examined the
potential interference to federal government radio systems that could result
from the deployment of BoPL, and identified appropriate
techniques that if applied, could potentially mitigate the interference. Some
examples of these techniques are:
·
Power control
·
Avoidance of locally used frequencies
·
Differential-mode signal injection
·
Filters and signal terminations to alleviate impedance mismatch
discontinuities
The NTIA reports are a set
of guidelines to service providers on how to conduct their interference
measurements. These reports are available online:
http://www.ntia.doc.gov/ntiahome/fccfilings/2004/bpl.
In June 2004, the White House called for the establishment of
technical standards to make possible new broadband technologies such as the use
of high-speed communications directly over power lines.
Meanwhile, in order for this technology to
be viable, some problems have to be solved, such as finding a suitable model
for the power line channel that incorporates signal degradation through the line
and by interference and noise sources, determining appropriate frequency
allocation schemes and acceptable transmission power levels to minimize
interference into existing services, and finally; selecting suitable
transmission schemes and countermeasures to effectively minimize the external
interference effects on the proposed system. It is important to remember that
in
[1]
P. Amirshahi and M. Kavehrad,
“High-Frequency Characteristics of
Overhead Multi-conductor Power Lines for Broadband Communications,”
IEEE Journal on Selected Areas in Communications, Vol. 24, No. 7, July 2006.
[2]
P. Amirshahi and M. Kavehrad,
“Transmission
Channel Model and Capacity of Overhead Multi-conductor Medium-Voltage
Power-lines for Broadband Communications,” IEEE Consumer
Communications & Networking Conference,
[3]
P. Amirshahi and M. Kavehrad,
“Medium
Voltage Overhead Power-line Broadband Communications; Transmission Capacity and
Electromagnetic Interference,” Proceedings of ISPLC 2005,
[4]
Paul
S. Henry, “Interference
Characteristics of Broadband Power Line Communication Systems Using Aerial
Medium Voltage Wires,” IEEE
Communications Magazine, pp. 92-98, April 2005.
[5]
P. Amirshahi and M. Kavehrad,
“System Design Considerations for High data
Rate Communications Over Multi-wire Overhead Power-lines,” The
VI IEEE International Workshop on Signal Processing Advances in Wireless
Communications,
[6]
P. Amirshahi, S.M. Navidpour and M. Kavehrad, “'Fountain Codes for Impulsive Noise Correction in Low-Voltage Indoor Power-line Broadband
Communications,” IEEE Consumer Communications & Networking
Conference, Las Vegas, Nevada, January 2006.
[7]
P. Amirshahi and M. Kavehrad,
“Broadband Access over Medium and Low Voltage Powerlines and use of White Light Emitting Diodes for
Indoor Communications,” IEEE Consumer Communications & Networking
Conference,
See also:
·
Scientific American: Broadband to the people
·
NetworkWorld: A
two-pin plug and you have broadband
·
The Energy Daily:
Repeaters are Key
·
Solution to the Global Digital Divide Problem
·
Black Issues in Higher Education: Penn State Engineers
Present Expanded View of Broadband by Power Lines
·
Penn-State Research News: Power Line Data
Transmission Capacity: Bigger Than DSL Or Cable
·
CICTR News: http://cictr.ee.psu.edu/cictrnews.htm
·
FCC Chairman
Powell kicks off his new regular AO blog:
Michael
Powell Joins the Blogosphere
·
·
Electronic Clipping: Alliance opts for interoperable powerline broadband specs
TV Interview:
Acknowledgments
This research is supported by the
AT&T Shannon Labs through a grant and by the CICTR of The Pennsylvania
State University.
Hybrid Wireless Access
Systems
The allocated bandwidth for RF FWA is adequate for both point-to-point high
capacity trunk lines and point-to-multipoint shared bandwidth last miles
connections. Furthermore, if broadband Wireless Optical links or Hybrid Optical & RF
Combined Wireless Links are used, there is a huge
and as yet unregulated optical spectrum available which is secure and easily
reusable, due to availability of focused optical beams.
Atmospheric-optical-wireless links are excellent means for extending the fiber
reach into rural areas.
Radio Frequency (RF) communications are generally reliable and well
understood but cannot support emerging data rate needs unless they use a large
portion of the precious radio spectrum. Free Space Optical (FSO) communications
[1] offer enormous data rates but operate much more at the mercy of the
environment. The perennial limitations of FSO communications are manifested in
the channel attributes of scintillation (optical turbulence) and path
obscurations. Both phenomena reduce the availability of the optical channel to
support reliable communications. Since RF paths are relatively immune to the
same phenomenology, combining the attributes of a high data rate but burst link
(FSO) with the attributes of a low data rate (by comparison) but reliable link
(RF) could yield attributes better than either one alone: high availability
with high data rates.
This is one of our
active areas of research.
{1] Lasers that transmit data at
over 1 gigabyte per second may be coming to your neighborhood, The FEATURE
Journal,
Acknowledgments
This project is a collaborative research
between the AT&T Shannon Labs and the CICTR of The Pennsylvania State
University.
10GBASE-T
Transmission over Standard Category-5 or 6 Copper Cable
With the increasing popularity of multimedia services supplied
over a fixed network, services such as: web browsing, video conferencing and video-on-demand,
it is only a matter of time before users will demand higher bandwidth LAN
access. Advances in signal processing and fast CMOS processing power have also
made it possible for users to afford high-resolution visual services. IEEE is
interested in specifying the next generation 10 Gbps
twisted pair Ethernet network (10GBASE-T) in the not too distant future. The
research focus here is on conceptual designs and demonstration of a 10GBASE-T
copper transmission system for distribution of a digital signal over ~100
meters of a standard CAT-5 or 6 copper cable. It is believed to be possible to
achieve this, using standard copper cable if we adopt vectored transmission on
4 pairs in presence of cross-talk and noise. The 10 Gigabit per second speed is
about 1/2 the theoretical capacity on these cables at 100 meters. This physical
layer design can be adopted in future 10 Gbps
Ethernet LANs where fast connection to server farms on campus settings is a
potential application of such access networks.
Our presentation to the IEEE 802.3 Standards Committee,
the 10GBASE-T Study Group can be downloaded from the 10GBASE-T Study Group
Meeting site at: http://www.ieee802.org/3/10GBT/public/nov03/index.html
Ø Nexans White Paper: Nexans efforts on 10Gbe over UTP
Ø Nexans White Paper: Dynamic Performance: Assessing Cabling Claims
for 10GBASE-T, Nexans, May 2004.
Ø Penn-State Research
News: Copper
wire shown to be competitive with fiber optic cable for LANS
Ø Eurek-Alert: Copper wire ……………..
Ø HimTimes: Copper
Wire……………
Ø Continuity Central: Copper wire broadband LANS shown to have advantages over fibre optic cable
Ø Today's focus: Cat-6 may go farther…………..
Ø
Wire and Cable
International Overview (page-3): Copper seen as
competition for FO cable
Ø Monitor: Copper wire competitive………….
Ø
The WAI Connection: Can copper
wire match……….
Ø
BrightSurf: Copper
wire shown to be competitive
Ø
Speed guide: Copper
wire………………
Ø
UOL Inovacao: Cobre pode substituir fibra óptica na transmissão de dados
Ø
CTFQ – O
Potal Oficial da……………
Ø
Business Week: Developments to watch
Acknowledgments
This research
is supported by the Pittsburgh Digital Greenhouse through a grant
from the
Fixed Wireless Access Systems;
Multimedia-Teleconferencing
Robust and Error-Resilient Multimedia Video-Teleconferencing
over UNII-Band
Fixed Wireless Channels
I.
Starting with H.263+ and H.323 standards for packet-video
compression encoding / decoding, appropriate measures are being added to make the
compression algorithms more error- resilient on Fixed Wireless Fading Channels.
II.
In applications involving image, video and other mixed media
transmissions, the channel as seen by the higher layers is not the same old
natural continuous-time physical channel. It is a modified channel due to the
error correction mechanisms used on the physical layer. Thus, the uncorrected
errors affect the design of video encoding algorithms.
A UNII-Band 5.8 GHz, frequency hopping digital radio, using an
adaptive signal constellation, on a metropolitan-area nearly Line-of-Sight
(LOS) radio link provides a wireless test-bed for Quality-of-Service (QoS) measurements. We are performing on-going status
monitoring of a nearly point-to-point radio link on the
UNII Link
Selected
Papers
·
J. Yun,
· K. Muhonen and M. Kavehrad, “Amplifier Linearization with Memory for Broadband Wireless Applications,” Proceedings of the Thirty-Fifth Asilomar Conference on Signals, Systems and Comput