1. A field effect transistor comprising:
a lower barrier layer which is placed on a substrate and which is made of AlxGa1-xN;
a channel layer which is placed on a surface of the lower barrier layer that is opposite to the substrate and which is made of GaN;
an upper barrier layer which is placed on a surface of the channel layer that is opposite to the lower barrier layer and which is made of AlyGa1-yN having an Al composition proportion exceeding an Al composition proportion of the lower barrier layer;
a source electrode and drain electrode which are placed on a surface of the upper barrier layer that is opposite to the channel layer;
an insulating layer placed on a region of the upper barrier layer, the region being in a surface of the upper barrier layer that is provided with the source electrode and the drain electrode, the region excluding a region provided with the source electrode and the drain electrode;
a gate electrode placed on the insulating layer; and
a region directly under the gate electrode having a recessed structure in which the insulating layer extends through the upper barrier layer to the channel layer.
2. The field effect transistor according to claim 1, wherein at least one portion of GaN making up the channel layer is negatively doped.
3. The field effect transistor according to claim 2, wherein the channel layer includes a first channel sub-layer located on the upper barrier layer side and a second channel sub-layer located on the lower barrier layer side, the n-type doping concentration of the first channel sub-layer is less than the n-type doping concentration of the second channel sub-layer, and the insulating layer is placed so as not to reach the second channel sub-layer.
4. The field effect transistor according to claim 3, wherein the first channel sub-layer is made of undoped GaN and the second channel sub-layer is made of negatively doped GaN.
5. The field effect transistor according to claim 2, wherein the channel layer includes a plurality of GaN sub-layers.
6. The field effect transistor according to claim 6, wherein the channel layer includes a first channel sub-layer located on the upper barrier layer side and a second channel sub-layer located on the lower barrier layer side, the n-type doping concentration of the first channel sub-layer is less than the n-type doping concentration of the second channel sub-layer, and the insulating layer is placed so as not to reach the second channel sub-layer.
7. The field effect transistor according to claim 6, wherein the first channel sub-layer is made of undoped GaN and the second channel sub-layer is made of negatively doped GaN.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A communication network, comprising:
a first wireless communication device;
a second wireless communication device that comprises a legacy station,
wherein the first wireless communication device and the second communication device are part of a wireless network,
wherein the first wireless communication device transmits a preamble field,
wherein the first wireless communication device transmits a legacy signal field after the preamble field, wherein the legacy signal field indicates (1) a time duration or (2) a length and a rate of at least a backwards-compatible burst transmission,
wherein the first wireless communication device transmits a plurality of paired fields after the legacy signal field, each paired field comprising a respective signal field and a respective service and protocol data unit field, wherein the backwards-compatible burst transmission comprises the plurality of paired fields, wherein the second wireless communication device decodes the legacy signal field, wherein the second wireless communication device interprets the backwards-compatible burst transmission as a single frame, and
wherein the first wireless communication device generates an interframe gap after the plurality of paired fields.
2. The communication network according to claim 1, wherein each service and protocol data unit field of the plurality of paired fields is encoded differently.
3. The communication network according to claim 1, wherein the plurality of paired fields are decoded if received by a burst-capable station.
4. The communication network according to claim 1, wherein the legacy signal field comprises a single legacy signal field.
5. The communication network according to claim 1, wherein the legacy signal field relates to the plurality of paired fields which forms at least a portion of a compact burst.
6. The communication network according to claim 1, wherein the legacy station or a burst-capable station determines a duration of a reservation of a communication medium.
7. The communication network according to claim 1, wherein the first wireless communication device generates the interframe gap of zero time.
8. The communication network according to claim 1, wherein the legacy signal field can be decoded by the legacy station and a station that supports a compact burst transmission format.
9. The communication network according to claim 1, wherein a backwards-compatible, burst-capable station decodes the legacy signal field, and wherein the backwards-compatible, burst-capable station individually decodes each paired field.
10. The communication network according to claim 1, wherein a remaining reservation time is cancelled if a reservation duration indicated in the legacy signal field has not been substantially used.
11. The communication network according to claim 1, wherein a reservation duration is trimmed as indicated in the legacy signal field, or wherein a remaining reservation time is cancelled as indicated in the legacy signal field.
12. The communication network according to claim 11, wherein the remaining reservation time is cancelled by sending a message that comprises an indication that a media access control (MAC) portion is of a NULL length or a ZERO length.
13. The communication network according to claim 11, wherein the remaining reservation time is cancelled by sending a message that comprises at least one of request-to-send (RTS) frame with a ZERO-length duration value and a clear-to-send (CTS) frame with a ZERO- length duration value.
14. The communication network according to claim 13, wherein the RTS frame or the CTS frame comprises information indicating a reservation holder.
15. The communication network according to claim 11, wherein the remaining reservation time is cancelled by sending a message that comprises a NULL-length frame or a ZERO-length frame.
16. The communication network according to claim 11, wherein the remaining reservation time is cancelled by sending a message that comprises at least one of (1) a physical layer preamble and a physical layer signal and (2) a physical layer signal field.
17. The communication network according to claim 11, wherein the remaining reservation time is cancelled by sending a message, wherein the message is eceived by a node in the wireless network that sends a reservation cancellation message to other nodes in the wireless network.
18. A wireless communication device, comprising:
a burst-capable station in wireless communication with other wireless stations in a wireless network,
wherein the burst-capable station transmits, via a plurality of antennas, a legacy signal field and a plurality of paired fields after the legacy signal field, each paired field comprising a respective signal field and a respective service and protocol data unit field, the respective service and protocol data unit fields being encoded differently, the legacy signal field indicating a reservation duration that covers at least the transmitting of the plurality of paired fields, wherein a legacy station in the wireless network decodes the legacy signal field and interprets the plurality of paired fields as a single large frame, wherein a burst-capable station decodes the paired fields,
wherein the burst-capable station generates an interframe gap after transmitting the plurality of paired fields, and
wherein the burst-capable station sends at least one of a ZERO-value frame, a NULL-value frame, a ZERO-length frame, a NULL-length frame and a ZERO-time reservation request to cancel or to trim the reservation duration.
19. The wireless communication device according to claim 18, wherein the wireless communication device is backwards compatible, and wherein the wireless communication device supports one or more of the following: diversity, beamforming and space-time coding.
20. A wireless communication system, comprising:
a first wireless communication device in wireless communication with a second wireless communication device,
wherein the first wireless communication device combines multiple frames of data into a single medium access and transmits a burst transmission comprising a legacy signal field and a plurality of paired fields, each paired field comprising a respective signal field and a respective service and protocol data unit field, the respective service and protocol data unit fields being encoded differently, the legacy signal field indicating a reservation duration that covers at least the transmitting of the plurality of paired fields, wherein the first wireless communication device generates an interframe gap after transmitting the plurality of paired fields, wherein the first wireless communication device transmits a message comprising at least one of a ZERO-value frame, a NULL-value frame, a ZERO-length frame, a NULL-length frame and a ZERO-time reservation request to cancel or to trim the reservation duration,
wherein, if the second wireless communication device includes a legacy station, then the second wireless communication device decodes the legacy signal field and interprets the plurality of paired fields as a single large frame, and
wherein, if the second wireless communication device includes a burst-capable station, then the receiver decodes the paired fields.