Accommodative monetary policies and a depressed yield environment support the case for an income approach to investing in 2015. While the discussion in the US has shifted to the timing of the first Fed rate hike, the current yield environment remains depressed. In Europe and Japan, policy remains highly accommodative (with further easing likely in Europe), reinforcing the global low-yield environment.

Low bond yields mean more diversified income approach warranted. Traditionally, investors focused on generating income would concentrate primarily on bond investments. However, with bond yields so low at the moment, opportunities for generating income are much more limited than has historically been the case. For instance, the 10-year US government bond currently yields just over 2%, compared with the average of over 4.3% between 2000 and 2010. Should yields return to more 'normal' levels, this would also hit bond values (when yields rise, bond prices fall). Therefore, it makes sense for investors to diversify their portfolios in order to balance the need for income today, income tomorrow and the protection of portfolio values.

There are three key broad asset classes for income investors - bonds, equities and non-core assets. We believe all three are important in generating sustainable income. Different income assets can be seen as generating different types of yield while assuming varying degrees of risk:

* Preservation yield: Lower yielding assets, important to manage an investor's risk profile.

* Maintenance yield: Higher yields, which generate the bulk of the investment income. This includes some assets that are capable of growing the yield over time.

* Aspiration yield: Highest yields which top up the investment's current yield, but with a higher degree of risk.

High dividend equity remains a key investment, in our opinion. Our core conviction remains for equities to outperform bonds in 2015. While high-dividend equity yields have fallen somewhat as prices have risen, we continue to like this asset class as a source of diversified income within a portfolio. The biggest risk to global equities is potentially higher volatility around the start of the US interest rate-hiking cycle. However, we expect the hikes to be gradual and well-advertised, which should limit any short-term volatility. There is also some evidence (albeit based on limited data points) that dividend equities tend to outperform the market during rate-hiking cycles.

New areas of focus within a diversified income allocation include the following:

* INR bonds: These bonds offer an attractive yield, while interest rate cuts should boost returns. Although the bonds are exposed to currency fluctuations, INR currency risks have declined following substantial accumulation in FX reserves by the central bank and a sharp fall in the current account deficit. This investment sits alongside our other preferred Asian local currency bond pick (CNY bonds), where yields are lower, but so are currency risks, in our opinion.

* Covered calls (equity): While we are still positive on global equities, we believe the probability of larger drawdowns (relative to recent history) over the coming year has increased. This strategy focuses on generating additional income through selling call options on equities that you own. As volatility rises, (normally when equity markets have already fallen) this increases the yield available from this strategy.

Adi Monappa is the head of asset allocation and portfolio solutions, wealth management group, Standard Chartered