Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2003-02-24
2004-11-16
Nguyen, Tony T. (Department: 2685)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S063100, C455S570000
Reexamination Certificate
active
06819943
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to the design and implementation of wireless rings and network of links in millimeter wave (MMW) line of sight wireless communications.
BACKGROUND OF THE INVENTION
It is normally necessary to obtain a “spectrum license” before using a frequency band for wireless communication. This is true of millimeter wave (MMW) frequencies, as it is for most other frequency bands. Spectrum licenses for MMW communications frequencies are issued by agencies responsible for management of the electromagnetic spectrum, and generally permit the use of two frequency bands for full-duplex (bi-directional, concurrent) communications—one band for transmitting (Tx) and one band for receiving (Rx).
FIG. 1
is a graphical representation of a typical single spectrum license
100
for full-duplex MMW communication comprising a first frequency band
102
and a second frequency band
104
. The first frequency band
102
(“Channel 1”) centers about a first frequency f
1
and has a first bandwidth &Dgr;f
1
. The second frequency band
104
(“Channel 2”) centers about a second frequency f
2
and has a second bandwidth &Dgr;f
2
. The second frequency f
2
is distinct and offset from the first frequency f
1
. The second bandwidth &Dgr;f
2
is typically substantially equal to the first bandwidth &Dgr;f
1
. In the context of the present invention, the first frequency band
102
is used for communication in a first direction between two “nodes” of a MMW communication network, and is generally indicated by a solid line with a left-pointing arrowhead, and the second frequency band
104
is used for communication in a second direction between the two nodes, and is generally indicated by a dashed line with a right-pointing arrowhead When referring to spectrum licenses in subsequent figures, dashed and solid lines will be used to represent the two distinct frequencies of a spectrum license, with arrowheads indicating the direction of communication, from transmitter to receiver. A bi-directional communication path between two adjacent nodes communicating over two distinct frequency bands is referred to as a “link,” and each link uses one spectrum license.
FIG. 2
is a block diagram of a multi-node MMW communication network
200
comprising a “chain” (or “ring”) of communication nodes
202
,
204
,
206
,
208
,
210
,
212
, and
214
. The system
200
employs multiple frequency licenses between multiple nodes.
The first node
202
(#1) communicates with the second node
204
(#2) over a link
216
via a first frequency band
216
a
and a second frequency band
216
b.
The first frequency band
216
a
is used for communications from the second node
204
to the first node
202
and the second frequency band
216
b
is used for communications from the first node
202
to the second node
204
.
The first node
202
(#1) communicates with the third node
206
(#3) over a link
218
via a first frequency band
218
a
and a second frequency band
218
b.
The first frequency band
218
a
is used for communications from the third node
206
to the first node
202
and the second frequency band
218
b
is used for communications from the first node
202
to the third node
206
.
The second node
204
(#2) communicates with the fourth node
208
(#4) over a link
220
via a first frequency band
220
a
and a second frequency band
220
b.
The first frequency band
220
a
is used for communications from the second node
204
to the fourth node
208
and the second frequency band
220
b
is used for communications from the fourth node
208
to the second node
204
.
The third node
206
(#3) communicates with the fifth node
210
(#5) over a link
222
via a first frequency band
222
a
and a second frequency band
222
b.
The first frequency band
222
a
is used for communications from the third node
206
to the fifth node
210
and the second frequency band
222
b
is used for communications from the fifth node
210
to the third node
206
.
The fourth node
208
(#4) communicates with the sixth node
212
(#6) over a link
224
via a first frequency band
224
a
and a second frequency band
224
b.
The first frequency band
224
a
is used for communications from the sixth node
212
to the fourth node
208
and the second frequency band
224
b
is used for communications from the fourth node
208
to the sixth node
212
.
The fifth node
210
(#5) communicates with the seventh node
214
(#7) over a link
226
via a first frequency band
226
a
and a second frequency band
226
b.
The first frequency band
226
a
is used for communications from the seventh node
214
to the fifth node
210
and the second frequency band
226
b
is used for communications from the fifth node
210
to the seventh node
214
.
Any ring/chain of “n” nodes can be implemented with at most “n” spectrum licenses, but in practice the required number of licenses is usually considerably smaller in point-to-point, line of sight MMW communication. In the system
200
of
FIG. 2
, some of the links
216
,
218
,
220
,
222
,
224
and
226
can use common spectrum licenses. The actual number of spectrum licenses used to implement a network of nodes is selected based upon the geometry of the network, the directionality of antennas, the local geometry of each node site and antenna polarization employed at the nodes. In combination, these parameters determine the amount of interference between nodes employing the same spectrum license. MMW receiving systems are frequency-selective enough that “cross-band” interference (interference between transmissions from different frequency bands) is negligible.
For example, if the antennas for the second node
204
(#2) and the fourth node
208
(#4) exhibit a high degree of electromagnetic separation from those of the third node
206
(#3) and the fifth node
210
(#5), then the links
220
and
222
can employ the same spectrum license. Because of the short wavelength of MMW frequencies, MMW antennas are inherently highly directional. As a result, a high degree of electromagnetic separation between nodes can be achieved in MMW when the antennas for those nodes are not aimed at one another. In some cases, the combination of antenna directionality and physical separation between independently communicating pairs of nodes ensures negligible interference therebetween, permitting re-use of a single spectrum license.
The basic building block of a multi-node point-to-point MMW network is a serial chain of three nodes, communicating using two links (which may or may use the same spectrum license, as discussed above) between a middle node and two adjacent nodes on opposite sides of the middle node. For example, the first node
202
, second node
204
and third node
206
of
FIG. 2
form such a chain (A chain of two nodes using only one spectrum license is a trivial case and does not account for the effects of inter-node interference that exists in longer chains of nodes. A three-node chain is the minimum size network subset that exhibits these interference effects.)
In a typical serial chain of three nodes, the two adjacent links often employ two different spectrum licenses. A necessary (but not sufficient) condition for the use of a common spectrum license is that the “middle” (intermediate) node of the three node chain transmits to both adjacent nodes using one frequency band (channel) of a spectrum license, and receives transmissions from both adjacent nodes via the other frequency band of the spectrum license. For example, consider a case where all of the links
216
,
218
,
220
,
222
,
224
and
226
of
FIG. 2
employ the same spectrum license. In this case, all of the first frequency bands
216
a,
218
a,
220
a,
222
a,
224
a
and
226
a
would be the same and all of the second frequency bands
216
b,
218
b,
220
b,
222
b,
and
224
b
would be the same. Node #1
202
transmits to nodes #2 and #3 (
204
and
206
) on the second frequency band (
216
b,
218
b
) and receives from nodes &
Friedman Mark M.
Millimetrix Broadband Networks Ltd.
Nguyen Tony T.
LandOfFree
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