US 8675570

I'll search for the specific patent number and any CAFC 2026 docket activity.

No CAFC docket activity surfaced. Let me check USPTO/litigation specifics.

Let me verify CAFC activity by party name and check the patent's term extension.

US Patent 8,675,570 — Summary

Search scope note: I searched for the specific number 8675570 / 8,675,570 across patent databases (Google Patents full text, uspto.report) and Federal Circuit 2026 materials (CAFC scheduled-cases listings, Fed Circuit Blog opinion/order digests, Justia CAFC opinions, and party-name queries). I did not locate any CAFC 2026 docket entry naming US 8,675,570 or Velocity Communication Technologies. I cannot confirm such an appeal exists or does not exist; treat the CAFC-2026 finding as "not found," not "confirmed absent." I also cannot run live USPTO PatentCenter/Assignment Center queries from here, so bibliographic data below is grounded in the Google Patents record (sourced from USPTO), cross-checked against the litigation complaint identified in search results.

Bibliographic data

Consistency check: 20 years from the 2008-03-24 filing date is 2028-03-24; adding 1,031 days (≈2.82 years) yields approximately 2031-01-19, which matches the listed adjusted expiration. The two figures are mutually consistent.

Abstract (as issued)

Techniques for bandwidth allocation in communication systems such as OFDM, OFDMA, or SC-FDMA systems to improve spectral efficiency and increase flexibility and adaptability with scalable single or multiple-carrier bandwidth allocation characteristics.

Plain-language overview of the independent claims

Claim 1 — carrier-group allocation with a "divides-everything" subcarrier spacing. A method for allocating spectrum in an OFDM/OFDMA/SC-FDMA system that: (1) divides available spectrum into a channel raster (the regulatory/system frequency grid) and multiple nominal channels, each carrying its own independent OFDM/OFDMA/SC-FDMA signal and each having a nominal channel bandwidth; (2) picks a single common subcarrier spacing that divides both the multiple nominal channel bandwidths and the channel raster evenly; and (3) places multiple carriers next to one another as a group in the same frequency band, with reduced or no guard bands between them. The same subcarrier spacing is aligned in frequency across the boundary between adjacent carriers so orthogonality is preserved and inter-carrier interference is reduced/eliminated, and the spacing must also evenly divide each of multiple different channel raster frequencies (e.g., across more than one band).

Claim 9 — channel/subchannel division with optional edge guard subchannels. A method that: (1) divides a frequency band into channels having nominal channel bandwidths; (2) divides each channel into subchannels made of multiple subcarriers at a common subcarrier spacing (frequency-aligned across adjacent carrier boundaries; capable of evenly dividing multiple different channel rasters); (3) selects the nominal channel bandwidths so each is evenly divisible into subchannels; and (4) may designate one or more edge subchannels at the spectral end of a channel as guard subchannels that transmit nothing (to meet spectral mask limits). This is the "keep a guard at the edge when you must" variant.

Claim 16 — back-to-back carriers with no inter-carrier guard band. A method that: (1) divides available spectrum into a channel raster and multiple nominal channels placed sequentially next to one another without guard bands between them, each carrying an independent OFDM/OFDMA/SC-FDMA signal; (2) assigns all subcarriers across those channels a common subcarrier spacing (one that evenly divides the channel raster) and aligns them across channels; (3) selects a sampling frequency equal to or greater than the given nominal channel bandwidth (or multiple such bandwidths); and (4) uses subcarriers within that bandwidth for transmission without assigning guard subcarriers at either end, with the common spacing frequency-aligned across adjacent carrier boundaries and capable of evenly dividing each of multiple different channel raster frequencies.

Dependent claims in brief: claims 2–3 (same or different nominal bandwidths; different bandwidths); claim 4 (bandwidths varied dynamically, slot-to-slot or symbol-to-symbol); claim 5 (side-by-side nominal carriers enabling full use of carrier bandwidth); claims 6–8 (spacing divides the channel raster; specifically 12.5 kHz or 10 kHz dividing 250 kHz and 200 kHz rasters for mixed-bandwidth multi-carrier deployment); claims 10–11 (16- or 20-subcarrier subchannels); claim 12 (DC subcarrier at carrier center); claim 13 (subchannels back-to-back across carriers with no unassigned subcarrier group); claims 14–15 (single common transmitter, or multiple frequency-synchronized transmitters).

Litigation context (adds specificity to the earlier litigation section)

Search results identify concrete case numbers and a 2026 wave of filings by Velocity Communication Technologies, LLC, asserting this patent (with others) — which is an addition to, not a contradiction of, the prior section:

• E.D. Tex. (Judge Robert W. Schroeder, III), filed 2025-07-09: 5:25-cv-00098 (OnePlus, lead case), -00099, -00100 (ASUSTeK), -00101, -00103, -00104 (HP), -00105, -00106, -00107, -00108, -00109.
• D. Del. (Judge Gregory B. Williams), filed 2025-07-09: 1:25-cv-00850 (Dell), 1:25-cv-00894, 1:25-cv-00912. In 1:25-cv-00850 the parties stipulated to a 30-day stay on 2026-04-17/20 pending a settlement agreement — so that action appears headed to resolution rather than appeal.
• E.D. Tex. 2026 filings: 5:26-cv-00103 (TCL, filed 2026-07-30), 5:26-cv-00104 (Charter, filed 2026-07-31), 5:26-cv-00105 (Hisense, filed 2026-07-31), 5:26-cv-00106 (Micro-Star International).
• The complaint characterizes the asserted portfolio as covering technologies incorporated into IEEE 802.11ax (Wi-Fi 6) and 802.11ax-based Wi-Fi 6E (OFDMA, UL MU-MIMO, BSS coloring, TPC).

Points of uncertainty

• CAFC 2026: No docket entry, opinion, or order naming this patent was found. Given active district-court cases still in early stages (and a settlement stay in the Dell action), it is unlikely an appeal has been docketed as of the current date, but I cannot state this with certainty.
• Assignee-of-record: The Google Patents listing shows Velocity Communication Technologies, LLC, with NCH 93, LLC as intermediate; I have not independently confirmed the current assignment record at USPTO Assignment Center.
• Patent-number discipline: Several search hits reference the patent using the spaced rendering "US 8 675 570 B2" in foreign-office citations; these refer to the same document (inventor "CAI SEAN"), and no distinct patent with that digit string appeared.

US patent 8675570 is involved in several litigation cases, primarily with Velocity Communication Technologies, LLC as the plaintiff.

Known litigation cases for US patent 8675570 include:

• Case 1:

  • Plaintiff(s): Velocity Communication Technologies, LLC
  • Defendant(s): ASUSTeK Computer, Inc.
  • Jurisdiction: Eastern District of Texas (E.D. Tex.)
  • Case Number: Not specified in available snippets.
  • Filing Date: Not specified in available snippets.
  • Outcome or Current Status: Active, as indicated by the general litigation status in the patent overview provided previously.

• Case 2:

  • Plaintiff(s): Velocity Communication Technologies, LLC
  • Defendant(s): Cisco Systems, Inc.
  • Jurisdiction: Eastern District of Texas (E.D. Tex.)
  • Case Number: Not specified in available snippets.
  • Filing Date: Not specified in available snippets.
  • Outcome or Current Status: Active, as indicated by the general litigation status in the patent overview provided previously.

• Case 3:

  • Plaintiff(s): Velocity Communication Technologies, LLC
  • Defendant(s): Aruba Networks, LLC.
  • Jurisdiction: Not specified in available snippets.
  • Case Number: Not specified in available snippets.
  • Filing Date: Not specified in available snippets.
  • Outcome or Current Status: Active, as indicated by the general litigation status in the patent overview provided previously.

• Case 4:

  • Plaintiff(s): Velocity Communication Technologies, LLC
  • Defendant(s): [Hewlett Packard Enterprise Company.](/litigations/by-defendant/Hewlett%20Packard%20Enterprise%20Company.)
  • Jurisdiction: Not specified in available snippets.
  • Case Number: Not specified in available snippets.
  • Filing Date: Not specified in available snippets.
  • Outcome or Current Status: Active, as indicated by the general litigation status in the patent overview provided previously.

The provided information from Unified Patents indicates these cases are listed under the patent number 8675570 in their NPE Litigation Database.

While the patent overview mentions multiple US cases filed in the Texas Eastern District Court and Delaware District Court in 2025, the detailed information (case numbers, filing dates, and specific outcomes beyond "active") for these additional cases is not fully available in the provided snippets. Furthermore, no specific CAFC 2026 docket entries directly naming US patent 8675570 were found in the search results.

Proceedings overview

Based on the available data and web searches, there are no AIA trial proceedings (Inter Partes Review, Post-Grant Review, or Covered Business Method) currently on file or that have been concluded for US Patent 8675570. This means the patent's claims remain untested by PTAB challenges.

Strategic summary

As of the current analysis, all claims (1-16) of US Patent 8675570 are UNTESTED by AIA trial proceedings. The patent has not undergone any PTAB review, meaning no claims have been canceled or sustained through these administrative processes.

Since no AIA trial proceedings have been instituted, there is no estoppel landscape under § 315(e)(2) for any petitioner (or their privies) with respect to prior-art grounds that could have been raised. All prior-art grounds remain potentially available for a future PTAB challenge, subject to statutory time bars (e.g., one year from service of a complaint alleging infringement for IPRs). There are no pattern signals, such as multiple IPR filings by the same petitioner or aggressive PTAB appeals by the patent owner, as there has been no PTAB activity for this patent.

Recommended next steps

Given the absence of any PTAB activity for US Patent 8675570, the following steps are recommended:

• For a potential defendant: Consider initiating an AIA trial proceeding (such as an Inter Partes Review) if facing assertion of this patent, especially if strong prior art exists. The absence of previous PTAB review means the patent's claims have not been "hardened" by surviving such challenges. A thorough prior art search should be conducted to identify potential grounds for invalidity under §§ 102 and/or 103. If a complaint alleging infringement has been served, be mindful of the one-year statutory deadline to file an IPR petition.

Inventors

• Sean Cai (employed by ZTE USA Inc. at the time of filing).

Original assignee

The original assignee, ZTE USA Inc., is a subsidiary of ZTE Corporation, a major Chinese telecommunications equipment and systems company. ZTE Corporation is known for developing and manufacturing telecommunications products and providing network solutions, indicating they ship products embodying their claims. ZTE USA Inc. is an operating company in the telecommunications sector. Their current status is operating.

Assignment timeline

• 2008-06-14 (executed) / recorded 2008-06-20 — Reel 021129/0752
  • Conveyance: Assignment
  • Assignor: Sean Cai
  • Assignee: ZTE (USA) INC.
  • Correspondent: Not explicitly listed in the provided patent text.
  • Context: Original assignment from inventor to the operating company.
• 2019-12-06 (executed) / recorded 2025-01-27 — Reel 070021/0541
  • Conveyance: Assignment
  • Assignor: ZTE (USA) INC.
  • Assignee: NCH 93, LLC (Minnesota)
  • Correspondent: Not explicitly listed in the provided patent text.
  • Context: Transfer-to-asserter (likely a shell entity based on name and subsequent transfer).
• 2025-01-29 (executed) / recorded 2025-01-30 — Reel 070067/0368
  • Conveyance: Assignment
  • Assignor: NCH 93, LLC (Minnesota)
  • Assignee: VELOCITY COMMUNICATION TECHNOLOGIES, LLC (Minnesota)
  • Correspondent: Not explicitly listed in the provided patent text.
  • Context: Transfer-to-asserter (another shell entity, part of a cascading transfer).

Timeline diagram

timeline
    title Ownership of US 8675570
    2008 : Filed by ZTE USA Inc
         : Assigned from inventor to ZTE
    2014 : Patent issued
    2019 : ZTE assigns to NCH 93 LLC
    2025 : NCH assigns to Velocity Comm Tech
         : Litigation initiated

NPE / troll-pattern signals

1. Shell-entity transfer — Present
   • NCH 93, LLC (Minnesota) acquired the patent from ZTE USA Inc. in January 2025 (recorded date). The name "NCH 93, LLC" is characteristic of a shell entity, often incorporated in states like Minnesota (or Delaware/Texas for patent assertion) without apparent product lines.
   • Velocity Communication Technologies LLC (Minnesota) acquired the patent from NCH 93, LLC in January 2025. This name, coupled with the rapid transfer and Minnesota incorporation, also suggests a shell entity dedicated to patent assertion rather than product development.
2. Known asserter in the chain — Present
   • While NCH 93, LLC and Velocity Communication Technologies LLC are not explicitly listed in the provided example NPE list, the patent text indicates that the "Family has litigation" with multiple US cases filed in Texas Eastern District Court and Delaware District Court in 2025. This demonstrates that the patent is actively being asserted, strongly suggesting the current owner, Velocity Communication Technologies LLC, is an NPE.
3. Repeat correspondent across the chain — Unclear
   • The correspondent attorney and firm information are not explicitly provided in the supplied patent text or Google Patents legal events for any of the assignment records (Reel 021129/0752, Reel 070021/0541, Reel 070067/0368).
4. Cascading transfers — Present
   • The patent was transferred from ZTE USA Inc. to NCH 93, LLC (executed 2019-12-06, recorded 2025-01-27, Reel 070021/0541) and then just three days later, from NCH 93, LLC to Velocity Communication Technologies LLC (executed 2025-01-29, recorded 2025-01-30, Reel 070067/0368). This rapid, consecutive transfer between two similarly named LLCs in a very short timeframe (less than 24 months, specifically 3 days between the final two recorded assignments) is a strong indicator of a cascading transfer typically seen in NPE operations.
5. Pre-litigation transfer — Present
   • The assignments to NCH 93, LLC and subsequently to Velocity Communication Technologies LLC were recorded in January 2025 (Reel 070021/0541 and Reel 070067/0368). Litigation cases for this patent family were filed in Texas Eastern District Court and Delaware District Court in 2025. The close proximity of these transfers to the initiation of litigation in the same year strongly suggests these transfers were arranged to enable or precede the assertion campaign.
6. Bankruptcy fire-sale — Not present
   • There is no indication in the provided information that ZTE USA Inc. or any other assignor in the chain filed for bankruptcy.
7. Privateering — Unclear
   • While ZTE USA Inc. transferred the patent, there is no direct evidence or explicit statement in the provided text to confirm that this is a privateering arrangement where Velocity Communication Technologies LLC is asserting on ZTE's behalf against competitors.
8. Defensive aggregator (anti-NPE) — Not present
   • The chain ends with Velocity Communication Technologies LLC, which is not a known defensive aggregator.

Verdict

NPE — high confidence

The pattern exhibits multiple strong signals: transfers to shell-like entities (NCH 93, LLC and Velocity Communication Technologies LLC per Reel 070021/0541 and 070067/0368), cascading transfers within days of each other (2025-01-27 and 2025-01-30 recorded dates), and these transfers immediately preceding or coinciding with active litigation filed in 2025. These elements combined point definitively to an NPE assertion strategy.

For verification, see the USPTO Assignment Center: https://assignmentcenter.uspto.gov/

To identify the most relevant prior art for US patent 8675570, I will examine the "Citations (13)" section provided in the patent text, as this lists the patents considered by the examiner during prosecution. I will then analyze each cited patent to determine its relevance and potential anticipation of the claims in US8675570.

Here is an analysis of the patent citations listed for US patent 8675570:

Most Relevant Prior Art for US Patent 8675570

The following prior art references were cited during the prosecution of US patent 8675570:

1. US5726978A

   • Full Citation: US5726978A, Telefonaktiebolaget L M Ericsson Publ., "Adaptive channel allocation in a frequency division multiplexed system"
   • Publication Date: 1998-03-10 (filed 1995-06-22)
   • Brief Description: This patent describes a method for adaptively allocating channels in a frequency division multiplexed system, where a base station allocates different frequency channels to mobile stations based on interference levels and required bit rates. While it deals with frequency allocation, it doesn't appear to explicitly address the specific problems of guard band elimination or common subcarrier spacing across multiple nominal channels in OFDM/OFDMA as detailed in US8675570.
   • Potential Anticipation: Less likely to directly anticipate the specific claims of US8675570, as its focus is on adaptive allocation rather than the fixed subcarrier spacing and guard band reduction techniques of 8675570.

2. EP0869647A2

   • Full Citation: EP0869647A2, Lucent Technologies Inc., "System of multicarrier modulation with dynamically scalable operating parameters"
   • Publication Date: 1998-10-07 (filed 1997-04-01)
   • Brief Description: This European patent application discusses a multicarrier modulation system with dynamically scalable operating parameters, which could potentially include varying subcarrier spacing or bandwidth. However, the explicit focus on evenly dividing nominal channel bandwidths and channel rasters with a common subcarrier spacing to eliminate guard bands, as in US8675570, would need to be thoroughly examined within its description.
   • Potential Anticipation: Potential for partial anticipation if its "dynamically scalable operating parameters" encompass the specific subcarrier spacing and channel raster alignment described in US8675570, particularly Claim 1 and Claim 16.

3. US5982327A

   • Full Citation: US5982327A, Motorola, Inc., "Adaptive array method, device, base station and subscriber unit"
   • Publication Date: 1999-11-09 (filed 1998-01-12)
   • Brief Description: This patent focuses on adaptive array methods for wireless communication, aiming to improve signal reception and reduce interference. It is primarily concerned with antenna array processing rather than the specific frequency domain allocation schemes, subcarrier spacing, and guard band elimination described in US8675570.
   • Potential Anticipation: Unlikely to directly anticipate the core claims of US8675570 due to a different technical focus.

4. EP1006668A1

   • Full Citation: EP1006668A1, Sony International (Europe) GmbH, "Dual frequency band transceiver"
   • Publication Date: 2000-06-07 (filed 1998-11-30)
   • Brief Description: This patent relates to transceivers operating in dual frequency bands. The description does not immediately suggest a direct relevance to the detailed subcarrier allocation, common subcarrier spacing for multiple carriers, and guard band reduction as claimed in US8675570.
   • Potential Anticipation: Less likely to directly anticipate the specific claims of US8675570.

5. US20040233838A1

   • Full Citation: US20040233838A1, Hiroaki Sudo, "Ofdm communication method and ofdm communication device"
   • Publication Date: 2004-11-25 (filed 2002-04-09)
   • Brief Description: This application discusses an OFDM communication method and device. Further review of its detailed specification would be necessary to determine if it teaches the specific approach of US8675570 regarding common subcarrier spacing to evenly divide nominal channel bandwidths and channel rasters across multiple carriers for guard band reduction.
   • Potential Anticipation: Possible, depending on the specifics of its OFDM communication method, particularly if it addresses inter-carrier interference through subcarrier alignment and guard band management.

6. US20050085236A1

   • Full Citation: US20050085236A1, Alcatel, "Method for subcarrier allocation and modulation scheme selection in wireless multicarrier transmission system"
   • Publication Date: 2005-04-21 (filed 2003-10-21)
   • Brief Description: This patent application describes methods for subcarrier allocation and modulation scheme selection in wireless multicarrier systems. While relevant to subcarrier allocation, it needs to be scrutinized for whether it explicitly teaches the uniform subcarrier spacing across nominal channel boundaries and channel rasters to eliminate guard bands, which is central to US8675570.
   • Potential Anticipation: Potential for partial anticipation if it teaches specific subcarrier allocation strategies that align with the claims of US8675570, especially Claim 1 and Claim 16, regarding uniform subcarrier spacing and guard band reduction.

7. US6904283B2

   • Full Citation: US6904283B2, Adaptix, Inc., "Multi-carrier communications with group-based subcarrier allocation"
   • Publication Date: 2005-06-07 (filed 2000-12-15)
   • Brief Description: This patent focuses on multi-carrier communications with group-based subcarrier allocation. The concept of grouping subcarriers is generally known in OFDMA. The key is whether it teaches the specific "common subcarrier spacing that divides multiple nominal channel bandwidths and the channel raster evenly" and the subsequent elimination of guard bands between carriers as explicitly claimed in US8675570.
   • Potential Anticipation: Possible, particularly for aspects of subcarrier allocation (Claims 1, 9, 16), but the specific method of eliminating guard bands by aligning subcarrier spacing across channel boundaries would need to be present.

8. US7158475B1

   • Full Citation: US7158475B1, Sony Corporation, "Transmitting apparatus and method and provision medium"
   • Publication Date: 2007-01-02 (filed 1999-03-12)
   • Brief Description: This patent describes a transmitting apparatus and method. The broad title requires a deeper dive into its specification to ascertain its relevance to the detailed bandwidth allocation and guard band reduction techniques of US8675570.
   • Potential Anticipation: Unclear without detailed analysis of its claims and description.

9. US20070036066A1

   • Full Citation: US20070036066A1, Motorola, Inc., "Method and apparatus for pilot signal transmission"
   • Publication Date: 2007-02-15 (filed 2005-08-15)
   • Brief Description: This application concerns pilot signal transmission in wireless communication systems. This area is distinct from the core innovations of US8675570 related to subcarrier spacing and guard band elimination for spectral efficiency in multi-carrier systems.
   • Potential Anticipation: Unlikely to directly anticipate the specific claims of US8675570.

10. US20070183520A1

    • Full Citation: US20070183520A1, Byoung-Hoon Kim, "Spectral shaping to reduce peak-to-average ratio in wireless communication"
    • Publication Date: 2007-08-09 (filed 2006-02-08)
    • Brief Description: This application discusses spectral shaping techniques to reduce the peak-to-average power ratio (PAPR) in wireless communication. While PAPR is a consideration in OFDM/OFDMA systems, this reference's primary focus on PAPR reduction through spectral shaping is different from US8675570's focus on guard band elimination and efficient subcarrier allocation.
    • Potential Anticipation: Less likely to directly anticipate the core claims of US8675570.

11. US20070242600A1

    • Full Citation: US20070242600A1, Neocific, Inc., "Methods and Apparatus for Multi-Carrier Communications with Variable Channel Bandwidth"
    • Publication Date: 2007-10-18 (filed 2004-05-01)
    • Brief Description: This patent application describes methods and apparatus for multi-carrier communications with variable channel bandwidth. This is highly relevant as US8675570 also deals with scalable bandwidth allocation and multi-carrier systems. It would be crucial to analyze whether "variable channel bandwidth" implicitly or explicitly includes the specific guard band elimination and common subcarrier spacing strategies across multiple nominal channels and channel rasters as defined in US8675570.
    • Potential Anticipation: Highly likely to be a significant prior art reference, potentially anticipating aspects of all independent claims (1, 9, 16) if its teaching of variable channel bandwidth and multi-carrier communication extends to the specific methods of subcarrier alignment and guard band reduction in US8675570. This reference should be closely scrutinized.

12. US20070258394A1

    • Full Citation: US20070258394A1, Yasuhiro Hamaguchi, "Communication Method and Radio Transmitter"
    • Publication Date: 2007-11-08 (filed 2004-10-29)
    • Brief Description: This application describes a communication method and radio transmitter. A detailed review of the specification is needed to assess its relevance to the specific bandwidth allocation and guard band reduction techniques of US8675570.
    • Potential Anticipation: Unclear without a detailed analysis of its claims and description.

13. US20080205351A1

    • Full Citation: US20080205351A1, Telefonaktiebolaget L M Ericsson (Publ), "Subcarrier Spacing Identification"
    • Publication Date: 2008-08-28 (filed 2007-02-23)
    • Brief Description: This application, though published after the priority date of US8675570 (March 23, 2007), was filed before the filing date of US8675570 (March 24, 2008) but after its priority date. Therefore, it would only be prior art under certain conditions (e.g., if US8675570 didn't claim priority to its provisional, which it did). However, assuming it was cited for its general teaching. It focuses on subcarrier spacing identification, which is a related but distinct concept from defining a common subcarrier spacing that evenly divides channel bandwidths and rasters to eliminate guard bands.
    • Potential Anticipation: Less likely to directly anticipate the core guard band elimination and precise subcarrier alignment aspects of US8675570, but its discussion of subcarrier spacing is broadly related. Note: It's important to confirm its effective prior art date relative to US8675570's priority date (March 23, 2007). Given the filing date (Feb 23, 2007) is before the priority date of US8675570, this would indeed be prior art.

Summary of Most Relevant Prior Art:

Based on the initial review of titles and descriptions, US20070242600A1 ("Methods and Apparatus for Multi-Carrier Communications with Variable Channel Bandwidth") appears to be the most relevant prior art. Its focus on "multi-carrier communications with variable channel bandwidth" directly touches upon the core area of innovation claimed in US8675570. A thorough examination of US20070242600A1's detailed specification and claims would be necessary to determine the extent of its anticipation of US8675570's claims, particularly regarding the precise methods of using a common subcarrier spacing to evenly divide nominal channel bandwidths and channel rasters for the purpose of eliminating or reducing guard bands and inter-carrier interference.

The obviousness of US patent 8675570 under 35 U.S.C. § 103 can be analyzed by considering combinations of prior art that would have motivated a person having ordinary skill in the art (PHOSITA) to arrive at the claimed invention. The patent itself identifies the core problem it seeks to solve: the spectral inefficiency and inter-carrier interference caused by existing OFDM, OFDMA, and SC-FDMA systems that employ guard subcarriers and have subcarrier spacings that do not evenly divide nominal channel bandwidths.

The priority date for US patent 8675570 is March 23, 2007.

I. PHOSITA's Motivation and Problem Recognition

A PHOSITA in the field of wireless communication systems, prior to March 23, 2007, would have been highly motivated to improve spectral efficiency and reduce inter-carrier interference in multi-carrier communication systems. The background of US patent 8675570 explicitly details the inefficiencies in prevailing standards like IEEE 802.16 or WiMAX, Ultra Mobile Broadband (UMB), and Long Term Evolution (LTE) systems, where guard subcarriers lead to wasted bandwidth and subcarrier spacing often cannot evenly divide nominal RF carrier bandwidths. For instance, the patent notes that for a 10 MHz nominal carrier bandwidth in a typical 802.16e design, about 8.8% of the bandwidth is wasted on guard subcarriers. This directly presents a known problem and a strong motivation for a PHOSITA to find solutions for more efficient spectrum utilization. The work by Sun (2001) on "Bandwidth-efficient wireless OFDM" further reinforces the long-standing motivation in the art to enhance bandwidth efficiency.

II. Combination of Prior Art References for Obviousness

The independent claims (Claims 1, 9, and 16) of US patent 8675570 largely center on choosing a common subcarrier spacing that evenly divides nominal channel bandwidths and channel rasters, enabling the reduction or elimination of guard bands and frequency alignment across adjacent carriers.

A. Combination for Claims 1 and 16 (Eliminating Guard Bands for Spectral Efficiency)

A compelling combination of prior art references to render Claims 1 and 16 obvious includes:

1. IEEE 802.16e-2005 Standard: This standard defines OFDMA (and OFDM) systems, including nominal channel bandwidths, subcarrier spacing (e.g., 10.9375 kHz for 10 MHz), and the inherent use of guard subcarriers as illustrated in FIG. 1A and discussed in the background of US8675570. It represents the baseline technology and the problem statement itself.
2. Sun, Yi, "Bandwidth-efficient wireless OFDM," IEEE Journal on Selected Areas in Communications, Nov. 2001: This non-patent literature explicitly teaches the goal of achieving "bandwidth-efficient wireless OFDM," underscoring the known desire in the field to optimize spectrum usage.
3. US20070242600A1 (Neocific): This reference teaches "Methods and Apparatus for Multi-Carrier Communications with Variable Channel Bandwidth," disclosing multi-carrier systems and the concept of variable channel bandwidths. This provides the context of managing multiple carriers, potentially of different sizes, in close proximity.
4. JP2001189657A (Toshiba): Discloses a "Frequency synchronization circuit," which teaches the importance and means for maintaining frequency synchronization, a prerequisite for coherent multi-carrier operations.

Motivation and Obviousness:

A PHOSITA, starting with an IEEE 802.16e-compliant OFDMA system and motivated by the well-known desire to improve bandwidth efficiency (Sun), would recognize the spectral waste caused by guard subcarriers and irregular subcarrier counts due to non-evenly dividing subcarrier spacing, as highlighted by US8675570 itself. In a multi-carrier deployment context (Neocific), the problem of inter-carrier interference (as depicted in FIG. 2A of US8675570) further strengthens the motivation to achieve better spectral alignment.

It would have been an obvious design choice for a PHOSITA to select a common subcarrier spacing that evenly divides the nominal channel bandwidths. This directly addresses the problem of "un-necessary guard subcarrier" and the "irregular number of available subcarriers for resource planning" identified in the patent's background. The patent explicitly states that "frequency efficiency is proportional to the number of used subcarriers over the maximum number of subcarriers within the carrier nominal bandwidth" (Eq. 4), making it an obvious objective to make these two numbers equal by appropriate subcarrier spacing selection. Tables 1 and 2 in US8675570, which illustrate exemplar subcarrier spacings (12.5 KHz and 10 KHz) that evenly divide various nominal carrier bandwidths and result in "0" guard subcarriers, effectively demonstrate this obvious design optimization.

Once individual nominal channels can be efficiently transmitted without internal guard bands due to this optimized subcarrier spacing, it would be a straightforward engineering decision in a multi-carrier system (Neocific) to place these channels "sequentially next to one another in frequency without guard bands in between," as claimed in Claim 16. To achieve this without inter-carrier interference, maintaining a "common subcarrier spacing of orthogonal subcarriers... aligned in frequency between boundaries of adjacent carriers" is a logical and necessary step. Frequency synchronization (Toshiba) would be understood as essential for such alignment in multi-carrier deployments to preserve orthogonality and minimize interference.

The requirement that the "common subcarrier spacing can evenly divide each of multiple different channel raster frequencies of one or more frequency bands" is also an obvious design consideration. Channel rasters are known regulatory or system-specific frequency grids. If a subcarrier spacing is chosen for spectral efficiency within a nominal channel, a PHOSITA would naturally attempt to select one that also aligns with or evenly divides common channel raster frequencies to facilitate compliant and flexible multi-carrier deployment. The patent itself provides examples of such subcarrier spacings (10 KHz and 12.5 KHz) that align with 250 KHz and 200 KHz channel rasters.

B. Combination for Claim 9 (Maintaining Guard Subchannels for Spectral Mask Requirements)

Claim 9 includes most elements of Claim 1, but specifically adds "using one or more edge subchannels at a spectral end of a channel as guard subchannels without transmitting signals."

Motivation and Obviousness:

While US patent 8675570 primarily aims to eliminate guard subcarriers for spectral efficiency, the patent itself acknowledges that in some deployments, "possible option not to transmit at the edge subcarriers in order to meet the spectral mask requirements." It further illustrates this in FIG. 7B, where "edge subchannels are assigned as guard subchannels which are not used for transmitting signals in order to meet the spectral mask requirements."

Given that prior art systems (like IEEE 802.16e) commonly employed guard subcarriers and filtering to manage out-of-band emissions, it would be an obvious engineering choice for a PHOSITA to retain guard subchannels at the edges of a nominal channel if required to comply with regulatory spectral mask requirements, even when implementing the improved subcarrier numerology for the main signal bandwidth. The motivation would be regulatory compliance and avoiding out-of-band emissions, which are common considerations in wireless system design. Therefore, combining the optimized subcarrier spacing and alignment techniques (as derived for Claims 1 and 16) with the known practice of using edge guard subchannels for spectral mask compliance (as taught by 802.16e and explicitly acknowledged as an option within the patent's own disclosure) would be obvious.

III. Conclusion on Obviousness

The combination of the IEEE 802.16e standard, the recognized need for bandwidth efficiency (Sun), the understanding of multi-carrier systems and variable bandwidths (Neocific), and general knowledge of frequency synchronization (Toshiba) would have motivated a PHOSITA to develop the techniques claimed in US patent 8675570. The selection of a common subcarrier spacing that evenly divides nominal channel bandwidths and channel rasters, leading to the reduction or elimination of guard bands and frequency alignment between adjacent carriers, represents an obvious design choice to solve known problems of spectral inefficiency and inter-carrier interference in OFDMA/OFDM systems. The inclusion of retaining guard subchannels for spectral mask compliance in Claim 9 is also an obvious design consideration, explicitly recognized within the patent's own disclosure as an alternative implementation for meeting regulatory requirements.